What You Can Do

A Citizen’s Guide to Lake Protection

What Is a Lake?

It’s not as simple as it may sound. A lake is a body of water, but it is also much more. A lake is an ecosystem, a community of interaction among animals, plants, microorganisms, and the physical and chemical environment in which they live. Critical to any lake ecosystem is the lake’s watershed, the surrounding land area that drains into that particular lake.

A complex interdependence has evolved among the organisms in a lake community. If one part of the ecosystem is disturbed, it affects other parts. A road, a housing development, a drainage project, a forest fire, acid rain or other such changes in the watershed can alter the delicate balance of the lake ecosystem.

Well-balanced lake ecosystems, however, do change from season to season and from year to year. Short- term events, like a single algal bloom (an unusual or excessive abundance of algae), may not necessarily signal a long-term problem. On the other hand, changes in land use in the watershed may not immediately have a visible effect on the lake. It may take a decade or more, for example, for changes in agricultural practices or urbanization to result in weed problems or fish kills.

Lakes Begin…and End

Most lakes were created by past geologic events. The vast lake-dotted and marshy landscapes found in North America were formed by glaciation in the relatively recent geologic past-10,000 to 20,000 years ago. Glaciers formed lake basins by gouging holes in loose soil or bedrock, by depositing material across streambeds or by leaving buried chunks of ice whose melting shaped lake basins. More recently, humans and other animals have created lakes by damming rivers.

Lakes constantly are undergoing slow evolutionary change, reflecting the changes that occur in their watersheds. Most are destined to fill in with sand, silt and topsoil washed in by floods and streams. These gradual changes in the physical and chemical components of the lake affect the development, competition and succession of many different plants and animals.

The natural process by which lakes form, evolve and disappear takes thousands of years. Human activities, however, can change these lakes-for better or worse-in less than a single generation.

How Do Lakes Work?

A necessary prerequisite for deciding how to protect a lake is developing a basic understanding of the physical, biological and chemical properties of a lake. These physical, biological and chemical properties-such as light, temperature, wind, precipitation and nutrients-affect plants, animals and the lake itself.

1. A Physical Look at Lakes

Lakes Form Layerse:  Lakes in temperate climates tens to stratify of form layers, especially during summer. This happens because the density of water changes as its temperature changes.Water is most dense at 39°F. Both above and below that temperature, water expands and becomes less dense. This means that in the spring, just before the ice melts, the water near the bottom will be at 39°F. Water above that will be cooler, approaching 32°F just under the ice. As the weather warms, the ice melts and the surface waters begin to heat up. Wind action and increasing density cause this surface water to sink and mix with the deeper water, a process called spring turnover.

As summer progresses, the temperature difference (and thus density difference) between upper and lower water becomes more distinct, and most lakes form three separate layers. The upper layer, the epilimnion, is characterized by warmer (lighter) water. The epilimnion is roughly equivalent to the zone of light penetration, where the bulk of productivity, or growth, occurs.

Below the epilimnion is another layer, the thermocline, in which the temperature declines rapidly. The thermocline is a narrow band of transition which helps to prevent mixing between the layers.

Below the thermocline lies water much colder than the epilimnion, called the hypolimnion. The hypolimnion is the zone of decomposition, where plant material either decays or sinks to the bottom and accumulates.

These temperature conditions will continue until fall. Then surface waters cool until they are as dense as the bottom waters and wind action mixes the lake. This is the fall turnover.

Lakes in the temperature climates tend to form layers. The epilimnion is roughly equivalent to the zone of light penetration where the bulk of productivity, or growth, occurs. The thermocline is a narrow band of transition which helps to prevent mixing between the layers. The hypolimnion is the zone of decomposition, where plant material either decays or sinks to the bottom and accumulates.

2. A Biological Look at Lakes

A lake can be divided into zones, or communities, of plants and animals. Extending from the shoreline is the littoral community, where aquatic plants are dominant. The size of this community depends on the extent of shallow areas around the lake. Water lilies, duckweed and submerged plants are abundant. These plants play an important role in the overall aquatic community by producing oxygen and providing food and shelter for insects, crustaceans, frogs, turtles and fish.

The area of open water is the limnetic community. This area is the habitat of phytoplankton (algae), zoopplankton (microscopic animals), and fish. The phytoplankton are very important, serving as the base of the lake’s food chain and producing oxygen.

The process by which green plants (including algae) produce oxygen from sunlight, water and carbon dioxide is photosynthesis. A pigment produced by the plants, chlorophyll, speeds this process. Since sunlight is very important to photosynthesis, oxygen will be produced only as deep as the sunlight penetrates. The depth of light penetration can be measured using a secchi disc.

Below the limnetic zone is the profundal community, where light does not penetrate. This zone or community is dominated by respiration, or oxygen consumption, rather than oxygen production. This zone corresponds roughly to the hypolimnion layer. The community in this zone consists of such organisms as bacteria and fungi. These organisms break down or consume (decompose) dead plants and animals that settle out of the waters above. This process consumes oxygen.

A lake can be divided into zones or communities. Extending from the shoreline is the littoral community, where aquatic plants are dominant. The area of open water is the limnetic community, the habitat of algae, microscopic animals and fish. The profundal community, where light does not penetrate, is the habitat of bacteria and fungi.

What can go Wrong in Lakes?

1. Eutrophication: The Weeds Take Over

Eutrophication is the process by which lakes are fertilized with nutrients (chemicals absorbed by plants and used for growth). It is a natural aging process, but human activities can speed it up, with more algae and weeds the result.

As nutrients such as nitrogen, phosphorus and potassium wash into lakes in runoff water or by soil erosion, they fertilize the lake, allowing algae and weeds to grow. As plants die and decompose, they accumulate on the lake bottom as muck. After hundreds or thousands of years of plant growth and decomposition, the character of a lake may more closely resemble a marsh or a bog. This aging is called natural eutrophication.

Lakes also can obtain nutrients from various human activities, which can literally make a lake “old” before its time. This accelerated aging is called cultural eutrophication. Nutrients washed from agricultural areas, storm water runoff from urban areas, municipal and industrial wastewater, runoff from construction projects and even recreational activities contribute to cultural eutrophication. When human activities increase the rate of nutrient and sediment enrichment of a lake, pollution is taking place.

Nutrient and pollution sources discharged to a lake from specific locations, like municipal and industrial wastewater outlets, urban stormwater outlets or other point sources are easy to identify, relatively easy to control through treatment projects, and have been the focus of much of the water pollution control work to date.

Nutrients and pollution sources that are not discharged from a pipe, but instead are washed off the land or seep into groundwater, are known as nonpoint sources of pollution or polluted runoff. These include runoff from agricultural fields and feedlots, leakage from septic tanks, nutrients from wetland drainage and storm water runoff, and others. Polluted runoff is best controlled through wise land use practices.

The natural process by which lakes form, evolve and disappear takes thousands of years. Human activities, however, can change these lakes — for better or worse — in less than a single generation.

2. Sedimentation: The Lake Fills In

Closely associated with eutrophication is sedimentation. Wind and water move soils from the surrounding watershed down into a lake. These soils settle on the bottom of the lake, and the lake becomes increasingly shallow. This process is again a natural part of lake aging, governed by gravity and the forces of rain and wind.

Sedimentation is greatly accelerated, however, by human activities that leave the soil exposed without vegetation for extended periods. Construction activities that leave soils bare, and intensive agricultural activities, such as plowing near lakes and streams of farming steep slopes, leave soils vulnerable to erosion.

This problem is best controlled through soil and water conservation practices and maintaining vegetation on soils.

3. Acidification: Air Pollution Affects Lakes

Acid rain occurs when air pollution from power plants, factories and cars mixes with cloud moisture to form acidic compounds, which eventually fall to earth as rain, snow or dust. Acid rain can change the chemical balance of a lake, sometimes with sever consequences. In Canada, New England and Scandinavia, thousands of lakes are now too acidic to support fish and other aquatic life.

4. Toxic Contamination: Excess Chemicals Contaminate Lakes

Several types of toxic substances may contaminate lakes: (1) industrial chemicals such as PCBs (polychlorinated biphenyls), metals, and solvents from point sources or runoff; (2) pesticides from agricultural runoff; (3) urban storm runoff containing metals and pesticides; and (4) air-deposited chemicals.

Toxic contamination may be dramatic-such as fish kills that eliminate part or all of a lake’s fish population. Less obvious impacts may include decreased reproduction or slower growth rates in fish.

One particularly dangerous impact is the bioaccumulation or build-up of toxic substances in fish flesh. The toxic effects may be passed on to humans eating the fish.

What Can You do to Take Care of Your Lake?

“Taking care of” your lake may require lake stewardship, lake management, lake restoration, or a combination of all three. These three terms-stewardship, management and restoration-are related but not interchangeable.

1. Lake Stewardship: An Attitude

Lake stewardship really is an attitude-it is the first important step in protecting a lake. Stewardship reflects an understanding that what we do on land and in the water affects the lake.

Stewardship centers on thoughtful consideration of the intricate lake ecosystem and the interdependence between the lake and its surrounding watershed. It takes into account the need to better balance our lives and lifestyles with the needs of our lakes.

In short, it is a recognition that lakes are vulnerable-that in order to make them thrive, we, both individually and collectively, must assume responsibility for their care.

2. Lake Management: A Process

Lake management is a process, and the second major step in lake protection. It reflects a willingness to study a lake, to assess its status and its needs, and to determine how best to maximize its potential as a thriving ecosystem.

Lake management can be as simple as fostering the practices of stewardship among lake homeowners and other interested individuals. Or it can include taking an active role in altering certain ecological relationships within the lake and its watershed to make a lake healthy and keep it healthy. Lake management can also include protecting the health of a lake ecosystem through a plan of preventive action.

Lake management, to be effective, requires the coordinated efforts of a group of individuals in the form of a lake association, sportsmen’s or conservation club, or some other organization.

3. Lake Restoration: Corrective Action

Lake restoration is an action directed toward a lake to “make it better.” It is one example of a lake management technique. The complexity and expense of this activity requires an organization with some authority over the lake and its watershed, such as lake improvement district or watershed district.

Lake Stewardship: What can an Individual do?

Good stewardship by the individual, whether a lake homeowner or simply a lake user, can do much to enhance the lake environment and serve as a beginning for sound lake management. Although most of the following comments are directed to lake homeowners, many also apply to those who live anywhere within a lake’s watershed. One of the most important things an individual can do is to get involved with other concerned citizens. Your collective efforts will yield the greatest dividends for you and the lake.

Here’s what you can do to protect and improve a lake by minimizing polluted runoff into the lake.

1. Siting the House and Other Facilities

  • Don’t let your house intrude upon the lake. Locate a new house and any future additions to meet horizontal setback and vertical elevation requirements and to avoid damage if the lake rises dramatically in the future. Preserve as much natural vegetation as possible between the house and the lake to filter sediments and nutrients out of surface runoff.
  • You’ll also need to consider other facilities, particularly wells and septic systems, when siting your house. The septic system should receive priority since adequate soil conditions are necessary for its proper functioning. Site evaluators and many sewage system installers can conduct soil borings and percolation tests and consult soil maps and data to determine the best location on your lot. Wells should be located upslope from sewage systems and be deep and cased whenever possible. A site sketch of your lot, drawn to scale, will help you decide the best locations for all facilities and is often required when obtaining permits.
  • Contact your county zoning officer to determine what permits will be needed and what standards must be met. Take a personal interest in meeting the regulations. Don’t leave the arrangements entirely to your contractors.
  • If a standard septic tank and drainfield system are unsuited for your lot, you may have to use an approved alternative system such as a mound system. On some lots a holding tank may be the only feasible system.
  • Make sure your contractors know which trees you want to save. Fence off areas to protect trees and roots from construction damage.
  • Don’t put a road or wide path down to the lake. Curve any path you do build to the lake. Consider a wooden stairway rather than a road if you need access along a steep slope.2. Altering the Waterfront
  • If you want a sandy beach for swimming, try to buy a lot with a natural beach. Sand dumped on the shore to create a beach can seriously affect the habitat of fish birds, frogs and aquatic insects.
  • Make waterfront equipment such as docks and boat houses as unobtrusive as possible. Avoid structures that require much tree clearing, excavating or filling.3. Modifying Yard Care
  • Think twice before putting in a lawn-you may not need one in a lake setting. Maintain as wide a buffer zone of natural vegetation as possible between the lawn and the water’s edge.
  • Minimize the use of pesticides, herbicides and fertilizers, which can harm the lake.
  • Don’t burn brush or leaves on a slope from which ashes can wash into the lake. 4. Taking Care of Your Septic System
  • Don’t let your septic system pollute the lake. Have your septic tank checked every other year and pumped when necessary.
  • Use nonphosphate detergents, wash only full loads of clothes, and use water- saving showers and toilets to avoid stressing your septic system. (In Minnesota, phosphates in household laundry detergents have been banned since 1977.)
  • Do not use a garbage disposal, and keep solvents, plastics, paper diapers and other similar products out of your septic system.Lake Management: What is it?Lake management requires a general knowledge of lake ecology, the causes of natural and cultural water quality problems, the techniques for restoring and protecting the lake, the legal and financial realities to be considered, and the administrative and technical resources available to concerned citizens.

Lake management begins with ecological awareness. Just as the art of the landscape painter begins with an understanding of the relationship between elements in the landscape, so must a lake be seen as part of an interdependent system of surface and subsurface flowing water and of plant and animal habitats that relate to, and rely on, each other.

Two Areas of Concern

Every lake is ecologically unique. Every management group will have a unique set of management objectives and a unique strategy for attaining them.

Lake management planners seeking the most effective way to arrest or reverse eutrophication face two general areas of concern:

The first addresses biological symptoms that arise in the lake-primarily from activities in the lake’s watershed. “Nutrient-rich” lakes can be made less “productive” through the use of watershed management practices. The cost depends on the extent of the problem.

In the second area of concern, the lake has reached a critical level. Nutrients accumulated in the lake continue to maintain excess productivity even with watershed management. The restoration of such a lake may require in-lake treatment as well as watershed management. The cost may be high.

Two Philosophies of Lake Management

Lake management approaches can be divided into two categories. One is the “quick-fix” approach. The other is long-term environmental management.

1. The “Quick-Fix” Approach

The “quick fix” in lake management is a short-term “solution,” such as the application of aquatic herbicides to quickly kill unwanted algae. Such chemical applications can go on year after year, becoming increasingly less effective if the underlying causes of the algal growth are ignored.

The “quick fix” treats the biological symptoms of a lake problem, but plant and fish productivity are directly dependent on the chemical and physical processes going on in and around the lake as well. These underlying factors must be the principal consideration in any plan to change the biology of a lake.

2. Long-Term Lake Management

Long-term lake management considers all of the environmental, cultural and biological factors affecting the lake and sets a higher priority on finding lasting solutions than on pursuing quick, cosmetic treatment of symptoms.A high quality, financially efficient environmental project takes time and begins with long-range planning. If immediate in-lake rehabilitation techniques are necessary, the community will need to be sure that such immediate rehabilitation efforts are followed by appropriate long-term management techniques.

Lake Management: What Can Be Done?

Lake management often begins with concern for a particular lake. The lake no longer lives up to someone’s expectations, whatever they might be.Deteriorated lakes can be restored, but the task is difficult. Understanding of lake ecosystems is incomplete, and, even when technical answers are available, they may be expensive to apply. Further, the results of a lake restoration project may not be apparent for years.

For these reasons, preventive action should be the first priority of most lake communities. If the lake is a valuable recreational asset, the primary objective should be to prevent further deterioration. Lake deterioration can be prevented by managing the watershed and by protecting the shoreline.Action to protect and restore a lake may be taken by individual lake property owners and by lake association, usually with the assistance of one or more government units.


Acid Rain: Rain with a higher than normal acid range. Caused when polluted air mixes with cloud moisture. Can make lakes devoid of fish.

Algal bloom: An unusual of excessive abundance of algae. Alkalinity: Capacity of a lake to neutralize acid.

Bioaccumulation: Build-up of toxic substances in fish flesh. Toxic effects may be passed on to humans eating the fish.

Biomanipulation: Adjusting the fish species composition in a lake as restoration technique.

Ecosystem: A community of iteration among animals, plants, and microorganisms, and the physical and chemical environment in which they live.

Epilimnion: Most lakes form three distinct layers of water during summertime weather. The epilimnion is the upper layer and is characterized by water and lighter water.

Eutrophication: The aging process by which lakes are fertilized with nutrients. Natural eutrophication will very gradually change the character of a lake. Cultural eutrophication is the accelerated aging of a lake as a result of human activities.

Eutrophic Lake: A nutrient-rich lake-usually shallow, “green” and with limited oxygen in the bottom layer of water.

Fall Turnover: Cooling surface waters, activated by wind action, sink to mix with lower levels of water. As in spring turnover, all water is now at the same temperature.

Hypolimnion: The bottom layer of lake water during the summer months. The water in the hypolimnion is denser and much colder than the water in the upper two layers.

Lake Management: A process that involves study, assessment of problems, and decisions on how to maintain a lake as a thriving ecosystem.

Lake Restoration: Actions directed toward improving the quality of a lake.

Lake Stewardship: An attitude that recognized the vulnerability of lakes and the need for citizens, both individually and collectively, to assume responsibility for their care.

Limnetic Community: The area of open water in a Lake providing the habitat for phytoplankton, zooplankton and fish.

Littoral Community: The shallow areas around a lake’s shoreline, dominated by aquatic plants. The plants produce oxygen and provide food and shelter for animal life.

Mesotrophic Lake: Midway in nutrient levels between the eutrpophic and oligotrophic lakes.

Nonpoint Source: Polluted runoff-nutrients and pollution sources not discharged from a single point: e.g. runoff from agricultural fields or feedlots.

Oligotrophic Lake: A relatively nutrient-poor lake, it is clear and deep with bottom waters high in dissolved oxygen.

pH Scale: A measure of acidity.

Photosynthesis: The process by which green plants produce oxygen from sunlight, waterand carbon dioxide.

Phytoplankton: Algae-the base of the lake’s food chain, it also produces oxygen.

Point Sources: Specific sources of nutrient of polluted discharge to a lake: e.g. stormwater outlets.

Profundal Community: The area below the limnetic zone where light does not pentrate. This are roughly corresponds to the hypolimnion layer of water and is home to organisms that break down or consume organic matter.

Respiration: Oxygen consumption
Secchi Disc: A device measuring the depth of light penetration in water.

Sedimentation: The addition of soils to lakes, a part of the natural aging process, makes lakes shallower. The process can be greatly accelerated by human activities.

Spring Turnover: After ice melts in spring, warming surface water sinks to mix with deeper water. At this time of year, all water is the same temperature.

Thermocline: During summertime, the middle layer of lake water. Lying below the epilimnion, this water rapidly loses warmth.

Trophic Status: The level of growth or productivity of a lake as measured by phosphorus content, algae abundance, and depth of light penetration.

Water Density: Water is most dense at 39°F and expands (becomes less dense) at both hither and lower temperatures.

Watershed: The surrounding land area that drains into a lake, river or river system.

Zooplankton: Microscopic animals