Habitat Restoration
Below is a four part series on pond excavation by Dr. Patrick Rusz, Director of Wildlife Programs.
Excavated Ponds as Fish Habitat
Although Michigan has an abundance of natural lakes and streams, resource managers estimate that as many as 50,000 artificial ponds have been built in our state. Landowners have created artificial water bodies for a great variety of reasons – including swimming, wildlife habitat, livestock watering, irrigation, and aesthetics – but fishing is cited by most landowners as their primary reason for wanting a pond.
Unfortunately, many ponds have not produced quality sport fishing, especially beyond about six years after construction. The reason is poor design and management caused by misinterpretation of information. There are lots of ‘bits and pieces` of information used by resource managers, heavy equipment operators, and others involved in pond construction, but for one reason or another, the resultant ponds often end up too shallow and are stocked with the wrong combinations of fish to offer much promise of long-term success.
The first important key in developing a good excavated pond for sport fishing is to plan for a water depth of at least 15 feet for warmwater species and about 18 feet if trout are to be stocked. Those depths are necessary in most areas of Michigan to ensure adequate oxygen throughout the year, provide a range of temperatures in the water column in summer, and provide the kind of space fish need for growth.
Shallower ponds tend to have periods of low oxygen in winter and summer, are more uniform in temperature, and more frequently produce stunted fish populations. Only part of the pond needs to be that deep, but the best ones for fishing generally have 15 feet of water under 25-50% of the pond surface.
Planning for a pond to be 15 feet deep and getting one or two different things. In the 1070s, I surveyed over 200 pond owners. Among other things, I asked them how deep their ponds were. I subsequently measured the maximum depth in a random sample of 25 of the ponds. I found that the ponds averaged 3 ½ feet shallower than the owner thought. One-third of the ponds were at least six feet shallower than their design depth. This discrepancy resulted in part because the contractor measured (or in most cases just estimated) the pond depth from the ground surface during excavation. Since almost all of the ponds were dug in sites that were dry at the surface, they never filled with water to the ground level. Some landowners also did not consider naturally-occurring drops in the water table during hot summers. This amounts to at least two feet in most areas of Central Michigan, and can be as much as four feet in some soil types. The obvious difference between actual water depth and depth of excavation is often overlooked!
Another reason ponds are built too shallow is that design depths are often compromised for economics. Contractors can’t dig as efficiently as they would like when they encounter heavy clay soils 10 feet or more below the ground. They often try, with some success, to talk the landowner into building a shallower pond.
Many publications state that ponds don’t need to be as deep when they have constant flow from creeks or springs. There is some truth to the statement because flowing water generally carries more oxygen as it can better exchange gases with the air above. There are small impoundments less than 10 feet deep that provide good fishing, but many of them require frequent removal of accumulated sediment carried-in by the stream.
Especially troubling are widespread misconceptions about what constitutes a “spring.” In my surveys, I talked with several dozen landowners who insisted their ponds were “spring fed” even though they never had any outflow except in times of very heavy rains. They recalled that during excavation they could see water gushing into the basin from several “springs.” What they actually saw was groundwater flowing into the dug hole from sandy “lenses” or gravelly “veins” common throughout Michigan. These sources put water in the hole only until the groundwater level is reached. Flow then stops and the pond level stabilizes. True springs of importance in pond design and management, on the other hand, represent persistent flows of groundwater from higher elevations that “feed” the pond and require an outlet.
Some landowners believe their ponds must be “spring fed” because they can feel cold water when they dive more than about six feet below the surface. What they are actually detecting is “thermocline,” the natural layering of warmer, less dense water over cooler water. That occurs in all deep, standing water in Michigan. The relationships among pond depth, bottom type, and plant growth are very important to fish management. Areas 15 feet or deeper support relatively little plant growth. But water less than 8 feet deep, especially over clay or organic soils, is almost sure to produce heavy plant growth. Although fish use plants for cover and the vegetation supports fish food organisms, too much growth can cause detrimental fluctuations in oxygen levels. Pond owners can generally get away with having shallow water under much of the pond surface only if the bottom is sandy or they commit to a rigorous program of weed control by mechanical or chemical treatments. Some people opt to place a foot or more of sand over shallow clay-bottomed areas as an alternative to digging deeper. The cost of spreading san is indeed sometimes less than to cost of additional excavation and disposal of clay, especially in small ponds.
Ponds with the necessary maximum depth and with shallow areas over clay or mucky bottoms minimized are generally capable of producing good fishing for many years if the right combinations of fish are stocked and maintained. In Michigan, there is little need to attempt to control the basic chemistry of the water. Adding lime, or calcium carbonate in any form, is recommended for ponds in the Southern U.S., but is usually detrimental in our state. No type of fertilizer should be added to Michigan ponds intended for sport fishing. Organic material, such as excessive amounts of tree leaves, should also be kept out of the ponds. There are few, if any, ponds in Michigan that can’t produce good fish populations because they are too infertile. On the other had, there are many that have too much growth of algae and other plants to be good fish habitat.
Only a few kinds of fish should be stocked in Michigan ponds. Trout, especially rainbows, can be planted in ponds that have a considerable amount of water less than 68 degrees during the summer. Ponds that are half an acre or larger and at least 18 feet deep will have water that could near the bottom of the deepest part in most summers. Some fish distributors claim that certain varieties of trout they sell can live in warmer water, but in ponds 15 feet deep or shallower there is a strong risk, at least in Central and Southern Michigan, of all types dying during hot weather. In suitable ponds, rainbow trout stocked as fingerlings (a few inches in size) will be about 15 inches long by the third summer. They will not reproduce in ponds, so their population must be maintained by stocking more trout of a size that will not be eaten by the remaining large ones. For that reason, only the initial stocking is with fingerlings, and maintenance stocking usually requires more expensive trout six inches or longer.
The best warmwater fish species for most Michigan ponds is the largemouth bass. They grow well and reproduce readily in ponds that have some sand over shallow water. Largemouth bass do well even if they are the only fish species in the pond. A widespread myth is that pond owners must stock one or more prey species for the bass. The ones most often pushed are bluegill, sunfish and various minnows. In truth, the bass-bluegill combination is often a disaster after the first four or five years. The bluegills actually prey more effectively on the bass, gobbling up their eggs and fry, and effectively shutting-down bass reproduction. Bass are generally unable to eat enough of the right sizes of bluegills to keep down the bluegill population, so the result is a stunted population of bluegills and a gradually aging population of bass. Worst still, the overabundant small fish eat-up the pond’s supply of tiny water fleas (zooplankton). Without a good population of algae-eating zooplankton, the algae community grows unchecked, giving the water undesirable green blooms.
Fishing out the bluegills by hook-and-line is impractical, and even intensive seining and removal of the stunted sunfish seldom corrects the problem. Fathead minnows are a better choice for stocking as a prey species for bass, but they usually must be restocked periodically. Bass eat such a variety of prey, including small bass, crayfish, tadpoles, frogs, and insects, that providing a fish prey species is often not necessary. Bass can be stocked in combination with trout in deep ponds without such serious problems.
Channel catfish will survive in Michigan ponds, but usually will not reproduce well. Growth rates are slow in Northern Michigan. They are very vulnerable to predation by bass and so only larger sizes can be stocked where there is an existing bass population. Many pond owners keep a few large catfish in their ponds as a sort of novelty, while their main focus is on bass management.
Fish distributors often recommend hybrid sunfish, usually bluegills crossed with pumpkinseed or redear sunfish, for Michigan ponds. But claims that they will grow faster without the stunting problems that beset bluegill populations are not reliable because the commercial stocks are often contaminated with fertile sunfish. The more familiar kinds of panfish common in our state – including yellow perch, crappies, green sunfish and rock bass – hurt bass reproduction and stunt just a badly as do bluegills.
Walleyes will survive in many ponds, but won’t reproduce, and grow slowly. Like catfish and northern pike, a few may have some value as “novelties” in a pond, but the walleye is a poor choice as the primary species.
Contamination of ponds after initial stocking is a major problem throughout Michigan. Within 10 years of construction, most ponds have at least a half dozen fish species the landowner never stocked. This has often been blamed on entry of fertilized fish eggs which clung to the feet of ducks and other birds. However, in each case where such contamination has been thoroughly investigated, it was found that neighborhood children or well-meaning adults had added the new fish species. People apparently find it hard to resist dropping a few fish in another’s pond, regardless if they have permission of the landowner. Ponds located near cities and suburbs get periodic, unsolicited “plantings” of many varieties of goldfish and other unwanted species from aquariums. Maintaining a good population of large bass that will eat the newcomers is the best means of reducing related problems.
With the right combination of depths and bottom types, Michigan ponds can support a modes amount of fish harvest and/or some excellent catch-and-release fishing. Feeding the fish commercial pellets in not recommended in most ponds because it adds nutrients to the water and spurs excessive plant growth. Without such supplemental feeding most Michigan ponds can support 50-100 catchable-sized bass or trout per surface acre. Adding crayfish, frogs, mayflies and water fleas (microcrustaceans such as Daphnia), is not necessary. These will find their ways into the pond if there is suitable habitat. Adding structure such as rocks and brush provides cover for fish, and cover and attachment sites for their food organisms. It may also boost spawning success of bass as well as catfish. However, many ponds with “clean” structure-free bottoms support good sport fishing.
Most problems in fish management begin when ponds are dug too shallow. Multiple uses such as swimming and providing wildlife habitat can best be accommodated by providing distinct areas for each use rather than by compromising on depth throughout the pond. More problems follow when the wrong fish species are stocked in an attempt to provide “something for everybody.” Even small children have little trouble catching bass in artificial ponds. The smaller bass tend to take bait about as readily as bluegills. The best pond designs and management strategies keep things simple.
Excavated Ponds as Wildlife Habitat
Standing water almost always attracts a great variety of wildlife. Regardless of its size or shape, a pond will draw song birds, raccoons, deer, and many kinds of water-dependent animals to a site. But excavated ponds that produce, not merely attract, wildlife in significant numbers have features that don’t occur by accident.
The best ponds for wildlife are shallow, with most of the basin less than two feet deep during the summer. They have some of the vegetation characteristics of natural wetlands –emergent plants like cattail near the shoreline, and submergent and floating-leaved species like stonewort and pondweed in the deeper areas. The amount of shoreline habitat – and thus area which can be colonized by cattail – can be maximized by creating an irregular-shaped pond rather than a circular or rectangular one. Wildlife biologists often use the term “shoreline development” to refer to the amount of irregularity in pond shape. Besides providing more area for cattail growth, irregular shorelines provide feeing and resting sites for many reptiles and amphibians intimately associated with the land/water surface. Shorebirds, waterfowl, deer, raccoons, and muskrats also utilize pond shoreline extensively.
Islands provide additional shoreline and are particularly good nesting sites for waterfowl and loafing sites for turtles and frogs. Several small ones will provide more shoreline than a single island of the same total area.
Creating a pond with good shoreline development is not difficult if the excavator has good knowledge of where the summer-time water level will be after the pond is built. Sometimes, however, elaborate schemes to provide for attractive bays and other features that maximize shoreline are rendered ineffective when water level drops so much that it simply forms a circular pool in the deepest part of the basin. Such problems can best be avoided by digging a series of test holes in summer in the area to be excavated. Regardless of soil type, most Michigan ponds stabilize very close to the ground water level in summer.
Soil type greatly influences the rate at which plants colonize and grow in excavated ponds. Shallow water over clay is usually inhabited by cattail, while bulrushes grow along sandy shorelines. Invasion by plants of high value to wildlife is generally much faster on clay bottoms than on sand. Adding a few inches of topsoil over sandy areas aids pant colonization, and a drawdown of the pond in late spring or early summer will also spur plant growth.
For ponds that can’t be drawn-down by pumping or some other means “spiking” the pond with soil from an older pond, wetland, or ditch will help. This is best done during construction when the material can be tucked-in and spread by machine. Lots of schemes to add organic material to ponds after they have tilled with water have been tried. Loading and spreading soil over the ice in winter, and scattering hay bales have been used with some success, but such methods are costly or require a lot of work.
As in the case of fish ponds, lime or fertilizer of any type should not be added to ponds intended for wildlife. This will likely lead to growth of algae that will out-compete desirable rooted plants.
Many nurseries now provide – for a considerable price – a variety of wetland/pond plants as seed or root stock. In my experience, planting nursery stock is seldom cost-effective. Suitable plants will eventually invade most ponds through natural processes if the right combination of soil and water depth is present. Planted stock is often out competed by invading species after a few years.
Wildlife use of a pond can be boosted greatly by constructing or installing many kinds of “microhabitats” used by particular wildlife species. Trees “hinge-cut” or cabled to the bank provide loafing areas for turtles and perch sites for wading birds such as great blue herons. Next boxes and elevated “hen houses” (see photos****) attract nesting wood ducks and mallards. In general, wildlife use is increased when some brush, logs, or rocks are placed in the pond.
It is not necessary to stock a pond with any type of wildlife. Frogs, turtles, crayfish, mayflies and other insects, and water fleas (microcrustaceans such as Daphnia) and all types of other animals will find their way into the pond if there is suitable habitat. If a wildlife pond has a hole five or more feet deep it might harbor fish year-round. But a fish population is not necessary for a pond to attract wildlife. Stunted populations of bluegills and other sunfish can, in fact, be counter-productive to wildlife by gobbling-up algae-eating water fleas and causing algae blooms that inhibit growth of more desirable plants. Carp are especially detrimental. They will roil the water, preventing growth of desirable plants.
Pond Excavation: The Construction Process
Excavating a pond is in many ways similar to building a house. In both cases, there is a seemingly endless sea of options and details. You could hire someone to take care of almost all aspects of the design and construction, but the better you can understand and guide the process, the more likely you will be pleased with the final product – and the bill.
As discussed in the previous articles in this series, ponds for fishing should have at least 25 percent of their area with water 15 feet deep or more, and shallow areas over clay or muck should be minimized. Ponds for wildlife feature water less than two feet deep in summer, and the bottom type is less important than in ponds for fishing. Of course, ponds can be excavated most economically where the water is closest to the ground surface. So, most prospective pond owners quickly focus on the lower-lying spot on their properties. The best pond sites are indeed often obvious, but it is a mistake to always look at the lowest spot. Sites at a little higher elevation that have mineral soils like sands or clays are often preferable to those with mucky soils or peat, unless one plans to remove all organic soil during construction. The groundwater table tends to follow the contours of the land and may be fairly close to the surface at elevations above the mucky basins.
Prospective pond owners are often advised to consult the modern soil surveys available from the federal Natural Resources Conservation Service for information about site suitability for ponds. The published soil surveys rank pond-suitable soils largely on the basis of how well they hold water. However, this has little relevance for excavated ponds that do not depend on water runoff. Depth to the groundwater is of most importance and can only be determined by direct observations in test holes.
It is critical to determine the typical summer groundwater elevation at a pond site prior to construction. Serious problems can occur when the groundwater elevation is not considered or assumed to be the same as in the spring. Heavy equipment operators usually measure their work from the ground. They typically equate a 15-foot-deep pond, but they are not the same! Since the summer groundwater level is often 4 feet or more below the spring level, even excavations in the lowest areas can produce ponds several feet shallower than intended. If a test hole shows the late summer water level three feet below the surface, an 18-foot-deep hole must be dug to provide a pond 15 feet deep. Although seemingly obvious, this basic information is frequently overlooked and is the cause of many after-project disputes between pond owners and contractors. Ponds that are too shallow to provide good sportfishing, and wildlife ponds that dry up in late summer are the frequent result of failure to determine groundwater levels and make it the basis of both design and construction contracts.
Another overlooked area in pond construction is planning what to do with all the excavated dirt. Many pond owners do not worry about this until the excavating equipment is at work. They are often amazed at, and sometimes overwhelmed by, the amount of dirt (spoil) generated during excavation. Faced with “running out of room” to place the dirt, they often decide to compromise on pond depth and/or pond size. In other cases, where all the related decisions are left to the contractor, pond owners may end up dismayed at the “mountains” of unsightly dirt that are left around their “dream pond.” It is extremely important that pond owners and their contractors discuss in detail how and where dirt will be placed.
The most cost-effective ponds are those in which dirt is moved only once. That is, it is placed at or very close to its final resting place with one lift or push by the excavating equipment. Deep ponds are normally dug by a backhoe or, where the groundwater movement into the hole is rapid, by a dragline. Shallow areas (less than about 5 feet deep) are often excavated by a bulldozer. The larger backhoes and most draglines have an effective reach of only about 50 feet. The maximum distance a bulldozer can push dirt cost-effectively is also about 50 feet. So, pond widths are typically 100 feet or less where cost-efficiency is important. To achieve greater widths, the dirt has to be moved twice or more, and costs escalate. Where dirt excavated by a backhoe or dragline has to be moved again, a bulldozer or “scraper” is often used because they can move piled dirt more efficiently.
Piled dirt often takes up to 20 percent more storage volume than dirt in the hole because it is not as compacted. Piles should not have side slopes steeper than 2:2 and be heavily seeded with grasses and legumes such as crown vetch to prevent erosion. Most pond owners have difficulty making piles higher than about 6 feet blend into the landscape and look attractive. So, where aesthetics is important, pond owners should set aside considerable land for the excavated dirt. If for example, a half-acre pond with a quarter-acre of 15-foot-deep water is created and the summer watertable is 3 feet below the ground, at least three-quarters of an acre of land is needed for spoil disposal for just the deep area. The shallow water area might easily require a dirt disposal area of another quarter-acre. So, the whole project would require an acre and a half.
Getting the most “bang for your buck” requires finding a competent, experienced contractor with the right equipment for your site and pond design. Projects are usually most cost-effective to hire an operator and machine(s) at a rater per running hour rather than a contract for the project at a fixed total cost. Prospective pond owners have a hard time accepting this well established fact. They incorrectly think they can get some free “insurance” against a costly project by demanding a “firm,” fixed-price bid. What they usually get instead is an inflated bid which allows for plenty of “contingencies.” The Michigan Wildlife Conservancy has considered fixed price bids for hundreds of earthmoving projects and in virtually every case saved a substantial amount of money by contracting by the hour. The only situation in which a pond construction contract by the hour might be more costly would be if the contractor was left entirely unsupervised and was blatantly dishonest in recording hours worked.
Solving Pond Management Problems
Good design helps maintain pond management troubles. But problems can occur even in ponds of the proper depth and bottom type. In ponds designed for sport fishing, the most common complaints are excessive growth of algae and other aquatic plants, stunted panfish, and poor water quality. Consultants and distributors of chemical and equipment tout dozens of “solutions,” but these can backfire. The cure may be worse than the illness if underlying causes are not addressed.
About one-quarter of pond owners are occasionally unhappy because of algae or other plants in their pond. This is especially common in shallow ponds with clay bottoms. The only lasting solution is to deepen the pond and/or cover the clay bottom with sand. If that is not practical, options include physically removing the pant growth, killing the plants with herbicides, or coloring the water with dye to reduce light penetration in the water.
In ponds less than 10 years old, the most prevalent ‘nuisance` plants are floating green and blue-green algae, stonewort (a plant-like algae form that grows attached to the bottom of the pond), and cattail. Older ponds often have even more kinds of plants.
Physical removal of the plants is generally a better short-term solution, because nutrients bound-up in the plant material are also removed. If the plants are killed by herbicides and left to decompose in the water, those nutrients are quickly recycled into the water and made available to new plant growth.
Herbicide treatment has another bad side effect. The dead plants sink to the bottom and accumulate in a mucky “ooze.” This forms a bottom favored by other nuisance plants. Ponds treated frequently for blue-green algae may accumulate several inches of ooze in just a few years. Many pond owners find the oozy bottom more troublesome than the plants.
You can use a rake to remove plants from small areas, but trash pumps or drags made of rolled fencing are more efficient in treating areas larger than a tenth of an acre. Physical removal of stonewort (Chara sp.) is particularly easy and sometimes reduces growth for several years. Floating types of algae usually come back much more quickly and may require annual or even semi-annual removal.
Cattail can best be controlled by cutting the new shoots below water level in springtime.
Chemical treatment of algae is done most often with copper sulfate or some other copper-based solutions such as Cutrine. Copper sulfate is quite toxic to trout and should not be used on trout ponds. It can also harm other fish species and fish food organisms if applied in high concentrations. Do not drop crystals into spawning beds or expose fish eggs to high dosages.
Using Cutrine reduces the risk to fish because the copper concentration is lower and application instructions are clear. Copper sulfate, on the other hand, is sold at agricultural supply outlets without instructions for use in ponds. It is usually applied by dragging a burlap bag full of crystals around the pond until they dissolve. If the crystals are simply thrown into the water, they may have little effect on the targeted plants.
If you use copper sulfate, you can minimize bad effects by applying it to a small area and waiting about seven days to see the results. Some stirring of the bottom water helps spread the chemical and maximize effectiveness. If the algae shows signs of stress (and you don’t see dead fish), the dosage may be about right. Alternately, you consult a professional to calculate dosage.
Copper-based chemicals are not effective on rooted aquatic plants, but there are many herbicides that can be used without effects on fish. Aquathol, diquat, and aquazine, are readily obtained for treating coontail, milfoil, and waterweed. Diquat is especially effective on cattail.
Aquashade, and other dyes are increasingly popular with pond owners. These reduce the amount of light available to plants, which reduces plant growth. However, reduced light means colder water. This may be a negative side effect it you want to use the pond for swimming.
Using fish or waterfowl to eat pond plants has been tried many times with disastrous results. These herbivores eat mostly beneficial plants, while rapidly recycling nutrients through their feces. Algae growth results, so one problem is traded for another. Plus, it is illegal to possess or bring into Michigan plant-eating exotic fish such as Asiatic grass carp.
You can achieve a small degree of biological algae control by limiting the numbers of small fish. That allows the populations of algae-eating-water-fleas to remain high and results in clearer water.
Controlling populations and size of fish can be difficult if a pond contains bluegills, other sunfish, or yellow perch. It is almost impossible to catch enough of these fish by hook-and-line to prevent stunting.
Some people have tried – without success – to control panfish by simply tossing a few northern pike or muskellunge into a pond. Even these notorious predators do not eat enough panfish to prevent stunted populations. Panfish control usually requires drastic measures such as drawdown of water level and seining with small-mesh nets. It is hard work, but it is much more effective than use of live traps.
Some pone owners opt to kill fish with a chemical such as rotenone. They then restock more suitable species after the water has detoxified. You will need a permit from the Michigan Department of Natural Resources if you choose this alternative and your pond has an outlet.
To avoid problems, get the help of a professional to plan chemical treatments of fish populations.
Prevention is better than treatment. Keep nutrients and organic matter out of ponds used for fishing and swimming. Tree leaves contribute much organic matter, so remove trees and large shrubs that grow close to the pond.
Canada geese and ducks contribute phosphorous and nitrogen to a pond, and geese can also serve as an intermediate host for the microscopic parasite that causes swimmer’s itch. Pond owners interested in swimming and fishing should not feed geese or otherwise encourage them to use their ponds. Occasional use of a pond by small numbers of ducks and geese does not cause water quality problems.
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Excavated Ponds as Fish Habitat
Although Michigan has an abundance of natural lakes and streams, resource managers estimate that as many as 50,000 artificial ponds have been built in our state. Landowners have created artificial water bodies for a great variety of reasons – including swimming, wildlife habitat, livestock watering, irrigation, and aesthetics – but fishing is cited by most landowners as their primary reason for wanting a pond.
Unfortunately, many ponds have not produced quality sport fishing, especially beyond about six years after construction. The reason is poor design and management caused by misinterpretation of information. There are lots of ‘bits and pieces` of information used by resource managers, heavy equipment operators, and others involved in pond construction, but for one reason or another, the resultant ponds often end up too shallow and are stocked with the wrong combinations of fish to offer much promise of long-term success.
The first important key in developing a good excavated pond for sport fishing is to plan for a water depth of at least 15 feet for warmwater species and about 18 feet if trout are to be stocked. Those depths are necessary in most areas of Michigan to ensure adequate oxygen throughout the year, provide a range of temperatures in the water column in summer, and provide the kind of space fish need for growth.
Shallower ponds tend to have periods of low oxygen in winter and summer, are more uniform in temperature, and more frequently produce stunted fish populations. Only part of the pond needs to be that deep, but the best ones for fishing generally have 15 feet of water under 25-50% of the pond surface.
Planning for a pond to be 15 feet deep and getting one or two different things. In the 1070s, I surveyed over 200 pond owners. Among other things, I asked them how deep their ponds were. I subsequently measured the maximum depth in a random sample of 25 of the ponds. I found that the ponds averaged 3 ½ feet shallower than the owner thought. One-third of the ponds were at least six feet shallower than their design depth. This discrepancy resulted in part because the contractor measured (or in most cases just estimated) the pond depth from the ground surface during excavation. Since almost all of the ponds were dug in sites that were dry at the surface, they never filled with water to the ground level. Some landowners also did not consider naturally-occurring drops in the water table during hot summers. This amounts to at least two feet in most areas of Central Michigan, and can be as much as four feet in some soil types. The obvious difference between actual water depth and depth of excavation is often overlooked!
Another reason ponds are built too shallow is that design depths are often compromised for economics. Contractors can’t dig as efficiently as they would like when they encounter heavy clay soils 10 feet or more below the ground. They often try, with some success, to talk the landowner into building a shallower pond.
Many publications state that ponds don’t need to be as deep when they have constant flow from creeks or springs. There is some truth to the statement because flowing water generally carries more oxygen as it can better exchange gases with the air above. There are small impoundments less than 10 feet deep that provide good fishing, but many of them require frequent removal of accumulated sediment carried-in by the stream.
Especially troubling are widespread misconceptions about what constitutes a “spring.” In my surveys, I talked with several dozen landowners who insisted their ponds were “spring fed” even though they never had any outflow except in times of very heavy rains. They recalled that during excavation they could see water gushing into the basin from several “springs.” What they actually saw was groundwater flowing into the dug hole from sandy “lenses” or gravelly “veins” common throughout Michigan. These sources put water in the hole only until the groundwater level is reached. Flow then stops and the pond level stabilizes. True springs of importance in pond design and management, on the other hand, represent persistent flows of groundwater from higher elevations that “feed” the pond and require an outlet.
Some landowners believe their ponds must be “spring fed” because they can feel cold water when they dive more than about six feet below the surface. What they are actually detecting is “thermocline,” the natural layering of warmer, less dense water over cooler water. That occurs in all deep, standing water in Michigan. The relationships among pond depth, bottom type, and plant growth are very important to fish management. Areas 15 feet or deeper support relatively little plant growth. But water less than 8 feet deep, especially over clay or organic soils, is almost sure to produce heavy plant growth. Although fish use plants for cover and the vegetation supports fish food organisms, too much growth can cause detrimental fluctuations in oxygen levels. Pond owners can generally get away with having shallow water under much of the pond surface only if the bottom is sandy or they commit to a rigorous program of weed control by mechanical or chemical treatments. Some people opt to place a foot or more of sand over shallow clay-bottomed areas as an alternative to digging deeper. The cost of spreading san is indeed sometimes less than to cost of additional excavation and disposal of clay, especially in small ponds.
Ponds with the necessary maximum depth and with shallow areas over clay or mucky bottoms minimized are generally capable of producing good fishing for many years if the right combinations of fish are stocked and maintained. In Michigan, there is little need to attempt to control the basic chemistry of the water. Adding lime, or calcium carbonate in any form, is recommended for ponds in the Southern U.S., but is usually detrimental in our state. No type of fertilizer should be added to Michigan ponds intended for sport fishing. Organic material, such as excessive amounts of tree leaves, should also be kept out of the ponds. There are few, if any, ponds in Michigan that can’t produce good fish populations because they are too infertile. On the other had, there are many that have too much growth of algae and other plants to be good fish habitat.
Only a few kinds of fish should be stocked in Michigan ponds. Trout, especially rainbows, can be planted in ponds that have a considerable amount of water less than 68 degrees during the summer. Ponds that are half an acre or larger and at least 18 feet deep will have water that could near the bottom of the deepest part in most summers. Some fish distributors claim that certain varieties of trout they sell can live in warmer water, but in ponds 15 feet deep or shallower there is a strong risk, at least in Central and Southern Michigan, of all types dying during hot weather. In suitable ponds, rainbow trout stocked as fingerlings (a few inches in size) will be about 15 inches long by the third summer. They will not reproduce in ponds, so their population must be maintained by stocking more trout of a size that will not be eaten by the remaining large ones. For that reason, only the initial stocking is with fingerlings, and maintenance stocking usually requires more expensive trout six inches or longer.
The best warmwater fish species for most Michigan ponds is the largemouth bass. They grow well and reproduce readily in ponds that have some sand over shallow water. Largemouth bass do well even if they are the only fish species in the pond. A widespread myth is that pond owners must stock one or more prey species for the bass. The ones most often pushed are bluegill, sunfish and various minnows. In truth, the bass-bluegill combination is often a disaster after the first four or five years. The bluegills actually prey more effectively on the bass, gobbling up their eggs and fry, and effectively shutting-down bass reproduction. Bass are generally unable to eat enough of the right sizes of bluegills to keep down the bluegill population, so the result is a stunted population of bluegills and a gradually aging population of bass. Worst still, the overabundant small fish eat-up the pond’s supply of tiny water fleas (zooplankton). Without a good population of algae-eating zooplankton, the algae community grows unchecked, giving the water undesirable green blooms.
Fishing out the bluegills by hook-and-line is impractical, and even intensive seining and removal of the stunted sunfish seldom corrects the problem. Fathead minnows are a better choice for stocking as a prey species for bass, but they usually must be restocked periodically. Bass eat such a variety of prey, including small bass, crayfish, tadpoles, frogs, and insects, that providing a fish prey species is often not necessary. Bass can be stocked in combination with trout in deep ponds without such serious problems.
Channel catfish will survive in Michigan ponds, but usually will not reproduce well. Growth rates are slow in Northern Michigan. They are very vulnerable to predation by bass and so only larger sizes can be stocked where there is an existing bass population. Many pond owners keep a few large catfish in their ponds as a sort of novelty, while their main focus is on bass management.
Fish distributors often recommend hybrid sunfish, usually bluegills crossed with pumpkinseed or redear sunfish, for Michigan ponds. But claims that they will grow faster without the stunting problems that beset bluegill populations are not reliable because the commercial stocks are often contaminated with fertile sunfish. The more familiar kinds of panfish common in our state – including yellow perch, crappies, green sunfish and rock bass – hurt bass reproduction and stunt just a badly as do bluegills.
Walleyes will survive in many ponds, but won’t reproduce, and grow slowly. Like catfish and northern pike, a few may have some value as “novelties” in a pond, but the walleye is a poor choice as the primary species.
Contamination of ponds after initial stocking is a major problem throughout Michigan. Within 10 years of construction, most ponds have at least a half dozen fish species the landowner never stocked. This has often been blamed on entry of fertilized fish eggs which clung to the feet of ducks and other birds. However, in each case where such contamination has been thoroughly investigated, it was found that neighborhood children or well-meaning adults had added the new fish species. People apparently find it hard to resist dropping a few fish in another’s pond, regardless if they have permission of the landowner. Ponds located near cities and suburbs get periodic, unsolicited “plantings” of many varieties of goldfish and other unwanted species from aquariums. Maintaining a good population of large bass that will eat the newcomers is the best means of reducing related problems.
With the right combination of depths and bottom types, Michigan ponds can support a modes amount of fish harvest and/or some excellent catch-and-release fishing. Feeding the fish commercial pellets in not recommended in most ponds because it adds nutrients to the water and spurs excessive plant growth. Without such supplemental feeding most Michigan ponds can support 50-100 catchable-sized bass or trout per surface acre. Adding crayfish, frogs, mayflies and water fleas (microcrustaceans such as Daphnia), is not necessary. These will find their ways into the pond if there is suitable habitat. Adding structure such as rocks and brush provides cover for fish, and cover and attachment sites for their food organisms. It may also boost spawning success of bass as well as catfish. However, many ponds with “clean” structure-free bottoms support good sport fishing.
Most problems in fish management begin when ponds are dug too shallow. Multiple uses such as swimming and providing wildlife habitat can best be accommodated by providing distinct areas for each use rather than by compromising on depth throughout the pond. More problems follow when the wrong fish species are stocked in an attempt to provide “something for everybody.” Even small children have little trouble catching bass in artificial ponds. The smaller bass tend to take bait about as readily as bluegills. The best pond designs and management strategies keep things simple.
Excavated Ponds as Wildlife Habitat
Standing water almost always attracts a great variety of wildlife. Regardless of its size or shape, a pond will draw song birds, raccoons, deer, and many kinds of water-dependent animals to a site. But excavated ponds that produce, not merely attract, wildlife in significant numbers have features that don’t occur by accident.
The best ponds for wildlife are shallow, with most of the basin less than two feet deep during the summer. They have some of the vegetation characteristics of natural wetlands –emergent plants like cattail near the shoreline, and submergent and floating-leaved species like stonewort and pondweed in the deeper areas. The amount of shoreline habitat – and thus area which can be colonized by cattail – can be maximized by creating an irregular-shaped pond rather than a circular or rectangular one. Wildlife biologists often use the term “shoreline development” to refer to the amount of irregularity in pond shape. Besides providing more area for cattail growth, irregular shorelines provide feeing and resting sites for many reptiles and amphibians intimately associated with the land/water surface. Shorebirds, waterfowl, deer, raccoons, and muskrats also utilize pond shoreline extensively.
Islands provide additional shoreline and are particularly good nesting sites for waterfowl and loafing sites for turtles and frogs. Several small ones will provide more shoreline than a single island of the same total area.
Creating a pond with good shoreline development is not difficult if the excavator has good knowledge of where the summer-time water level will be after the pond is built. Sometimes, however, elaborate schemes to provide for attractive bays and other features that maximize shoreline are rendered ineffective when water level drops so much that it simply forms a circular pool in the deepest part of the basin. Such problems can best be avoided by digging a series of test holes in summer in the area to be excavated. Regardless of soil type, most Michigan ponds stabilize very close to the ground water level in summer.
Soil type greatly influences the rate at which plants colonize and grow in excavated ponds. Shallow water over clay is usually inhabited by cattail, while bulrushes grow along sandy shorelines. Invasion by plants of high value to wildlife is generally much faster on clay bottoms than on sand. Adding a few inches of topsoil over sandy areas aids pant colonization, and a drawdown of the pond in late spring or early summer will also spur plant growth.
For ponds that can’t be drawn-down by pumping or some other means “spiking” the pond with soil from an older pond, wetland, or ditch will help. This is best done during construction when the material can be tucked-in and spread by machine. Lots of schemes to add organic material to ponds after they have tilled with water have been tried. Loading and spreading soil over the ice in winter, and scattering hay bales have been used with some success, but such methods are costly or require a lot of work.
As in the case of fish ponds, lime or fertilizer of any type should not be added to ponds intended for wildlife. This will likely lead to growth of algae that will out-compete desirable rooted plants.
Many nurseries now provide – for a considerable price – a variety of wetland/pond plants as seed or root stock. In my experience, planting nursery stock is seldom cost-effective. Suitable plants will eventually invade most ponds through natural processes if the right combination of soil and water depth is present. Planted stock is often out competed by invading species after a few years.
Wildlife use of a pond can be boosted greatly by constructing or installing many kinds of “microhabitats” used by particular wildlife species. Trees “hinge-cut” or cabled to the bank provide loafing areas for turtles and perch sites for wading birds such as great blue herons. Next boxes and elevated “hen houses” (see photos****) attract nesting wood ducks and mallards. In general, wildlife use is increased when some brush, logs, or rocks are placed in the pond.
It is not necessary to stock a pond with any type of wildlife. Frogs, turtles, crayfish, mayflies and other insects, and water fleas (microcrustaceans such as Daphnia) and all types of other animals will find their way into the pond if there is suitable habitat. If a wildlife pond has a hole five or more feet deep it might harbor fish year-round. But a fish population is not necessary for a pond to attract wildlife. Stunted populations of bluegills and other sunfish can, in fact, be counter-productive to wildlife by gobbling-up algae-eating water fleas and causing algae blooms that inhibit growth of more desirable plants. Carp are especially detrimental. They will roil the water, preventing growth of desirable plants.
Pond Excavation: The Construction Process
Excavating a pond is in many ways similar to building a house. In both cases, there is a seemingly endless sea of options and details. You could hire someone to take care of almost all aspects of the design and construction, but the better you can understand and guide the process, the more likely you will be pleased with the final product – and the bill.
As discussed in the previous articles in this series, ponds for fishing should have at least 25 percent of their area with water 15 feet deep or more, and shallow areas over clay or muck should be minimized. Ponds for wildlife feature water less than two feet deep in summer, and the bottom type is less important than in ponds for fishing. Of course, ponds can be excavated most economically where the water is closest to the ground surface. So, most prospective pond owners quickly focus on the lower-lying spot on their properties. The best pond sites are indeed often obvious, but it is a mistake to always look at the lowest spot. Sites at a little higher elevation that have mineral soils like sands or clays are often preferable to those with mucky soils or peat, unless one plans to remove all organic soil during construction. The groundwater table tends to follow the contours of the land and may be fairly close to the surface at elevations above the mucky basins.
Prospective pond owners are often advised to consult the modern soil surveys available from the federal Natural Resources Conservation Service for information about site suitability for ponds. The published soil surveys rank pond-suitable soils largely on the basis of how well they hold water. However, this has little relevance for excavated ponds that do not depend on water runoff. Depth to the groundwater is of most importance and can only be determined by direct observations in test holes.
It is critical to determine the typical summer groundwater elevation at a pond site prior to construction. Serious problems can occur when the groundwater elevation is not considered or assumed to be the same as in the spring. Heavy equipment operators usually measure their work from the ground. They typically equate a 15-foot-deep pond, but they are not the same! Since the summer groundwater level is often 4 feet or more below the spring level, even excavations in the lowest areas can produce ponds several feet shallower than intended. If a test hole shows the late summer water level three feet below the surface, an 18-foot-deep hole must be dug to provide a pond 15 feet deep. Although seemingly obvious, this basic information is frequently overlooked and is the cause of many after-project disputes between pond owners and contractors. Ponds that are too shallow to provide good sportfishing, and wildlife ponds that dry up in late summer are the frequent result of failure to determine groundwater levels and make it the basis of both design and construction contracts.
Another overlooked area in pond construction is planning what to do with all the excavated dirt. Many pond owners do not worry about this until the excavating equipment is at work. They are often amazed at, and sometimes overwhelmed by, the amount of dirt (spoil) generated during excavation. Faced with “running out of room” to place the dirt, they often decide to compromise on pond depth and/or pond size. In other cases, where all the related decisions are left to the contractor, pond owners may end up dismayed at the “mountains” of unsightly dirt that are left around their “dream pond.” It is extremely important that pond owners and their contractors discuss in detail how and where dirt will be placed.
The most cost-effective ponds are those in which dirt is moved only once. That is, it is placed at or very close to its final resting place with one lift or push by the excavating equipment. Deep ponds are normally dug by a backhoe or, where the groundwater movement into the hole is rapid, by a dragline. Shallow areas (less than about 5 feet deep) are often excavated by a bulldozer. The larger backhoes and most draglines have an effective reach of only about 50 feet. The maximum distance a bulldozer can push dirt cost-effectively is also about 50 feet. So, pond widths are typically 100 feet or less where cost-efficiency is important. To achieve greater widths, the dirt has to be moved twice or more, and costs escalate. Where dirt excavated by a backhoe or dragline has to be moved again, a bulldozer or “scraper” is often used because they can move piled dirt more efficiently.
Piled dirt often takes up to 20 percent more storage volume than dirt in the hole because it is not as compacted. Piles should not have side slopes steeper than 2:2 and be heavily seeded with grasses and legumes such as crown vetch to prevent erosion. Most pond owners have difficulty making piles higher than about 6 feet blend into the landscape and look attractive. So, where aesthetics is important, pond owners should set aside considerable land for the excavated dirt. If for example, a half-acre pond with a quarter-acre of 15-foot-deep water is created and the summer watertable is 3 feet below the ground, at least three-quarters of an acre of land is needed for spoil disposal for just the deep area. The shallow water area might easily require a dirt disposal area of another quarter-acre. So, the whole project would require an acre and a half.
Getting the most “bang for your buck” requires finding a competent, experienced contractor with the right equipment for your site and pond design. Projects are usually most cost-effective to hire an operator and machine(s) at a rater per running hour rather than a contract for the project at a fixed total cost. Prospective pond owners have a hard time accepting this well established fact. They incorrectly think they can get some free “insurance” against a costly project by demanding a “firm,” fixed-price bid. What they usually get instead is an inflated bid which allows for plenty of “contingencies.” The Michigan Wildlife Conservancy has considered fixed price bids for hundreds of earthmoving projects and in virtually every case saved a substantial amount of money by contracting by the hour. The only situation in which a pond construction contract by the hour might be more costly would be if the contractor was left entirely unsupervised and was blatantly dishonest in recording hours worked.
Solving Pond Management Problems
Good design helps maintain pond management troubles. But problems can occur even in ponds of the proper depth and bottom type. In ponds designed for sport fishing, the most common complaints are excessive growth of algae and other aquatic plants, stunted panfish, and poor water quality. Consultants and distributors of chemical and equipment tout dozens of “solutions,” but these can backfire. The cure may be worse than the illness if underlying causes are not addressed.
About one-quarter of pond owners are occasionally unhappy because of algae or other plants in their pond. This is especially common in shallow ponds with clay bottoms. The only lasting solution is to deepen the pond and/or cover the clay bottom with sand. If that is not practical, options include physically removing the pant growth, killing the plants with herbicides, or coloring the water with dye to reduce light penetration in the water.
In ponds less than 10 years old, the most prevalent ‘nuisance` plants are floating green and blue-green algae, stonewort (a plant-like algae form that grows attached to the bottom of the pond), and cattail. Older ponds often have even more kinds of plants.
Physical removal of the plants is generally a better short-term solution, because nutrients bound-up in the plant material are also removed. If the plants are killed by herbicides and left to decompose in the water, those nutrients are quickly recycled into the water and made available to new plant growth.
Herbicide treatment has another bad side effect. The dead plants sink to the bottom and accumulate in a mucky “ooze.” This forms a bottom favored by other nuisance plants. Ponds treated frequently for blue-green algae may accumulate several inches of ooze in just a few years. Many pond owners find the oozy bottom more troublesome than the plants.
You can use a rake to remove plants from small areas, but trash pumps or drags made of rolled fencing are more efficient in treating areas larger than a tenth of an acre. Physical removal of stonewort (Chara sp.) is particularly easy and sometimes reduces growth for several years. Floating types of algae usually come back much more quickly and may require annual or even semi-annual removal.
Cattail can best be controlled by cutting the new shoots below water level in springtime.
Chemical treatment of algae is done most often with copper sulfate or some other copper-based solutions such as Cutrine. Copper sulfate is quite toxic to trout and should not be used on trout ponds. It can also harm other fish species and fish food organisms if applied in high concentrations. Do not drop crystals into spawning beds or expose fish eggs to high dosages.
Using Cutrine reduces the risk to fish because the copper concentration is lower and application instructions are clear. Copper sulfate, on the other hand, is sold at agricultural supply outlets without instructions for use in ponds. It is usually applied by dragging a burlap bag full of crystals around the pond until they dissolve. If the crystals are simply thrown into the water, they may have little effect on the targeted plants.
If you use copper sulfate, you can minimize bad effects by applying it to a small area and waiting about seven days to see the results. Some stirring of the bottom water helps spread the chemical and maximize effectiveness. If the algae shows signs of stress (and you don’t see dead fish), the dosage may be about right. Alternately, you consult a professional to calculate dosage.
Copper-based chemicals are not effective on rooted aquatic plants, but there are many herbicides that can be used without effects on fish. Aquathol, diquat, and aquazine, are readily obtained for treating coontail, milfoil, and waterweed. Diquat is especially effective on cattail.
Aquashade, and other dyes are increasingly popular with pond owners. These reduce the amount of light available to plants, which reduces plant growth. However, reduced light means colder water. This may be a negative side effect it you want to use the pond for swimming.
Using fish or waterfowl to eat pond plants has been tried many times with disastrous results. These herbivores eat mostly beneficial plants, while rapidly recycling nutrients through their feces. Algae growth results, so one problem is traded for another. Plus, it is illegal to possess or bring into Michigan plant-eating exotic fish such as Asiatic grass carp.
You can achieve a small degree of biological algae control by limiting the numbers of small fish. That allows the populations of algae-eating-water-fleas to remain high and results in clearer water.
Controlling populations and size of fish can be difficult if a pond contains bluegills, other sunfish, or yellow perch. It is almost impossible to catch enough of these fish by hook-and-line to prevent stunting.
Some people have tried – without success – to control panfish by simply tossing a few northern pike or muskellunge into a pond. Even these notorious predators do not eat enough panfish to prevent stunted populations. Panfish control usually requires drastic measures such as drawdown of water level and seining with small-mesh nets. It is hard work, but it is much more effective than use of live traps.
Some pone owners opt to kill fish with a chemical such as rotenone. They then restock more suitable species after the water has detoxified. You will need a permit from the Michigan Department of Natural Resources if you choose this alternative and your pond has an outlet.
To avoid problems, get the help of a professional to plan chemical treatments of fish populations.
Prevention is better than treatment. Keep nutrients and organic matter out of ponds used for fishing and swimming. Tree leaves contribute much organic matter, so remove trees and large shrubs that grow close to the pond.
Canada geese and ducks contribute phosphorous and nitrogen to a pond, and geese can also serve as an intermediate host for the microscopic parasite that causes swimmer’s itch. Pond owners interested in swimming and fishing should not feed geese or otherwise encourage them to use their ponds. Occasional use of a pond by small numbers of ducks and geese does not cause water quality problems.
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