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Wisconsin Lakes FAQ

Frequently asked questions about lakes are answered on this page.

Water Levels and Drought

Does drought make blue-green algae worse?

There are two aspects of drought, heat and lack of moisture. Blue-green algae need nutrients, and cell growth and division increases as the water temperature increases. Nutrients come from runoff or from internal cycling from bottom sediments under certain conditions. Biological activity, such as cell growth and division, also increases exponentially with an increase in water temperature (biological activity increases 2 to 10 times with every degree of temperature).

In shallow bodies of water, sediments tend to be a ready source of nutrients – especially when the lake, pond or reservoir alternates between a stratified and un-stratified state. If the shallow lake or flowage is filled with rooted vascular plants (lake weeds), the water body typically responds by becoming more weedy, which may result in the water remaining clear and not as prone to algae blooms. If rooted lake plants are not present, planktonic algae growth explodes (blooms) until it is limited by either lack of water clarity (often self-shading) or the amount of nutrients available (less likely because of internal recycling).

In deeper waters (lakes that remain stratified throughout the summer), nutrients in the bottom sediments tend to be isolated from the surface waters where blue-green algae grow. However, deep, stratified lakes are not necessarily immune from blue-green algae issues. Warm water temperatures, lots of sunlight and stratification can lead to blooms, especially by nitrogen-fixing species. However, these blooms are less due to drought than to heat, sunlight and calm weather.

With less water flowing into flowages and reservoirs, the residence time of water in the pool increases. Slower moving water, along with increased temperatures, gives algae more opportunity to grow (algae typically need about 10 days of residence time).

Does the drought make Cladophora worse?

Cladophora, which grows in Lake Michigan, is a little bit different than blue-green algae. Since it grows on the lake bed, it needs clear water, but growth (cell division) is still a function of water temperature. High water temperatures increase biological activity and potentially (and likely) increase the growth rate of Cladophora. And while greater growth of Cladaophora doesn't mean more toxins, what it does mean is that more ends up on the beach, causing much higher bacterial counts which is a problem.

Why are water levels on my lake lower?

Low water levels are occurring in many places throughout the state and the reasons why vary according to the type of lake and circumstances. Lakes where water levels are controlled by a dam or other structure may not experience as drastic a drop as natural glacial kettle lakes common to northern Wisconsin and the central sands area. These lakes typically have water levels that are controlled by the elevation of the groundwater table, which in turn reflects the amount of rain water and snow melt that soaks into the ground and eventually reaches an aquifer -- minus the amount of groundwater discharging from the aquifer to lakes, rivers and wetlands and public and private water wells. Lower water tables occur if less water enters the aquifer or more is taken out, or both. A drought, changes in land use that allow less water to soak into ground, increases in pumping -- all can affect groundwater table levels, and in turn, lake levels. Often, it's a combination of all three: lean water years due to natural conditions like a drought are exacerbated by human actions; people withdraw more water, or pave over more land and destroy wetlands, decreasing the water reaching aquifers. Groundwater monitoring well records in some areas indicate that water levels today are nearing the low levels seen in the late 1950s to mid-1960, and which contrast to the high peaks seen in the early 1990s.

What causes water levels to go up and down?
Lake water level down.

Low lake water level

Lake water levels can fluctuate naturally due to rain and snowfall, which varies widely from season to season and year to year. While some lakes with streams running into them show the effect of rainfall almost immediately, others, such as seepage lakes, may not show the effect for months. Seepage lakes are landlocked water bodies that do not have a stream coming into or out of them but get most of their water from precipitation or runoff, supplemented by groundwater. Seepage lakes are the most common type of lakes in Wisconsin and many of them in northern Wisconsin are now experiencing lower water levels. Although changes in water levels may be perceived as a problem for property owners, it is natural for lakes to go up and down in cycles that are decades long.

Are low water levels bad for lakes?
Fassett's Locoweed

Fassett's Locoweed

The short answer is no. In fact, periodic low water conditions can be beneficial for lake ecosystems. It consolidates sediments, allows new plants to colonize the lake bed and it provides habitat for rare plants and shorebirds. In fact, one of our rarest shoreline plants, Fassett's Locoweed, is dependent upon periodic fluctuations of water levels to grow. This plant is only found in a handful of lakes on the planet (all in Wisconsin) and all of these lakes are subject to wide fluctuation in water levels. When water levels return, this expansion of plants becomes habitat for fish and wildlife, removes nutrients from water, and can increase water clarity. However, human actions that cause water levels to drop farther than this natural variation, or prevent the lake from returning to normal conditions, may harm the lake and its inhabitants over the long-term.

Is it OK to "clean up" my beach or remove vegetation on the exposed lake bed during low water periods?

In general, it is best to avoid disturbing the exposed lake bed. Shorelines and shallow areas of lakes play a vital role in providing habitat for fish and wildlife and for protecting water quality. A diverse native plant community provides the best habitat and defends against invasive species getting established. Until water levels return to normal, it is important for shoreline owners to avoid inadvertently harming exposed lakeshore areas.

There are some activities which may be necessary to maintain access, control invasive species, and reduce nuisance accumulations of biological material. Learning more about beach maintenance may help you do these activities in a way that minimizes harm to exposed lakeshore areas.

Most activities conducted on the exposed lake bed including beach grooming and cutting or chemically treating plants are regulated by the DNR, but there are a few activities that don't require a permit. For example, some minor vegetation management (except for wild rice) and other activities done by hand do not require permits from the DNR. Please be careful to avoid cutting any legally protected threatened or endangered plant species, which are located on the lakebed, which is public property.

The following activities require a permit: cutting an area larger than 30 feet wide, driving a motor vehicle on the lakebed, tilling, and chemically treating vegetation if the area is wet. The permits are designed to assure that the activity does not damage the lake or the sensitive exposed habitat. Learn more about permits.

Can anything be done to restore water levels (or remove excess water)?

On lakes with connecting streams or dams or other water level control structures, modifications may be considered to temporarily raise or lower the water level due to extreme conditions. However, permanent changes in water levels have huge implications for downstream property owners and users and are often very controversial. Establishing or changing levels on a lake with a water control structure will require DNR approval.

Lakes without natural outlets are even more difficult to address. Pumping water into a seepage lake can be expensive and results in very little change in the water level, as most of the water is basically recycled back to the local groundwater system.

What about high water levels?

High water levels can boost the amount of nutrients from runoff and flooded lakeshore soils, as well as create health problems with flooded septic systems and private wells. Fluctuating water levels can also increase shoreline erosion.

Getting rid of excess water is complex and may not be feasible, especially if the surrounding landscape and waterways are also flooded, or at high levels. Generally, permits are required to pump or divert water either from the lake itself or from the outlet stream if the purpose is for bringing back or maintaining the normal level of your lake. Contact your local water management specialist for more information.

Changing levels on a lake with a water control structure (e.g., a dam) will require DNR approval.

Water Quality

I want to buy lake property and want clear water. Where should I look?

It's important for people to know what they want their property to look like and how they want to use it, and then find a property that matches that vision. There are several online resources to get you started, particularly if water clarity is one of your priorities.

  • UW-Madison's will allow you to look at a map of Wisconsin and see which lakes tend to be clearer and to also investigate a specific lake.
  • Check out a recent water quality report for lakes in a specific county, based on data collected by the more than 1,000 Citizen Lake Monitoring volunteers who collect water quality data for a favorite lake.
  • Look at our online DNR lake maps and make sure that what you buy is what you want.

There may be limitations on the kinds of modifications an owner can make along the shoreline or in the water adjacent to the shoreline to protect the public interest. Property on a bay, for instance, may never naturally provide a nice sandy lake bottom for swimmers. Organic material may build up on the lake floor, giving it a "mucky" bottom with lots of aquatic vegetation. This provides critical habitat for fish and aquatic life. To help you wade through all of the considerations, review Extension Lake's Choosing the Right Waterfront Property publication.

What causes the blue-green scum you see on some lakes?

While true algae are an important part of the food chain, so called "blue-green" algae, are largely inedible to other aquatic organisms. "Blue-green algae" are actually photosynthetic bacteria that can proliferate and form blooms in lakes with excessive amounts of nutrients such as phosphorus and nitrogen. Nuisance algae blooms can be especially pronounced in warm water on hot, calm summer days. These blooms may look like blue or green paint and release noxious odors as the algae decomposes. Blue-green algae may produce toxins which can irritate swimmers' skin; in some cases, these toxins have killed animals such as dogs, cattle and waterfowl that have consumed large amounts of the water containing the toxins.

General rule: When you see conditions like this avoid swimming in the water until it clears up, and keep your animals out of the water as well. We can't eliminate blue-green algae - they're an inherent part of the overall algal community in many lakes. To control the intensity and frequency of blue-green algal blooms, the best thing to do is reduce the amount of nutrients entering the lake. Lawn fertilizer, runoff from cities, cultivated farm fields, feedlots, construction sites and many other sources all contribute phosphorus to our lakes. The response to reducing nutrient levels will not be immediate, but it is the best long-term solution.

What causes the foam on my shoreline?

In most instances the "foam" we see on the surface of our lakes and streams is natural, and while it's not aesthetically pleasing, it's harmless. The foam is created when natural organic compounds, such as those from decomposing plants and animals, are mixed with air as a result of wind and waves, or as water flows through rapids or over a dam. The foam often will collect on a downwind or downstream shore. In some cases, the foam appears after a bloom of a species of algae called a diatom, which has silica-based shells that break down.

What causes that yellowish powder or dust in my lake water?

The material you are seeing in your lake water (and probably all over your dock and boat as well) is most likely pine pollen. It's very common to see this material in late spring to summer. After becoming waterlogged, the pollen sinks to the bottom. This is a natural event and shouldn't affect the overall water quality of your lake.

What causes that "root beer" color in some lakes?

Sometimes described as root beer, coffee, tea or bog stain, such coloring is natural for many waters in northern Wisconsin. The coloration is not harmful and results from incompletely dissolved organic materials, sometimes referred to as tannins, which come from the decomposition of wetland plants in the watershed of the lake. Often, the greater the amount of wetlands in the watersheds, the darker the color of the water. Since the predominant land type in the watersheds of northern Wisconsin lakes is often a mixture of forests and wetlands, this can result in many lakes having this dark coloration.

What causes that turquoise color in some lakes?

Lakes with this coloration are often referred to as "marl lakes" and usually have very good water quality. Their lakebeds typically consist of marl, a mixture of clay, sand and limestone, which has a soft texture. These lakes also tend to be "hard-water" lakes, those with higher concentrations of calcium, magnesium and bicarbonate that can bind excess nutrients, such as phosphorus, and limit algal growth. The turquoise color is caused by the backscattering of light from the calcium carbonate floc suspended in the water and the high reflection of the light-colored (nearly white) marl lakebed. This backscattering is predominately blue-green in appearance versus the more green or yellow appearance seen in lakes with more suspended organic materials and sediments.

What causes that milk-like substance to appear near the shore on my lake?

The white, milky-looking substance is most likely a "whiting" or sudden appearance of calcium monocarbonate (CaCO3) or calcite due to increased photosynthesis from algae or aquatic plants. This is a naturally occurring phenomenon associated with dissolved inorganic carbon concentrations in lake water. In high concentrations, calcite (also called marl) can accumulate on beaches and lake beds in some lakes. This can be associated with an algae bloom in backwater or protected inlets of lakes.

What causes that green floating stuff in my lake that looks like fluffy clouds or cotton candy?

It's probably filamentous algae, sometimes called "moss" or "pond scum." This is a common and troublesome aquatic plant that forms dense, hair-like mats in shallow water where sunlight reaches the bottom of the pond or lake. As the algae grows, it produces oxygen that gets trapped in the entangled strands of algae. This entrapped oxygen makes the algae buoyant and causes it to rise to the surface of the pond or lake. Some of the more common forms of filamentous algae can be identified by their texture, although microscopic examination is usually required for exact recognition. Cladophora feels "cottony," while spirogyra is bright green and very slimy to the touch, and pithophora (or "horse hair") has a very coarse texture like horse hair or steel wool. The best method for homeowners to remove filamentous algae is to rake out the floating clumps and limit the nutrients that reach the water from your property. You can compost these piles or use them in your garden as mulch. Remember, chemical control does require a permit from DNR.

Human Health

What causes swimmers itch?

Swimmer's itch is caused by a blood fluke common in waterfowl. The itching is caused when the fluke, while in the immature stage of its life cycle, mistakes you for its primary host -- waterfowl -- and burrows into your skin. Aside from the annoying itching, swimmer's itch is harmless to humans. The irritation can last from two days to several weeks, depending on the individual's susceptibility. Preventive measures can be taken, and there are no permanent effects from swimmer's itch.

Is my lake safe to swim in?

Recent surveys indicated that 60 percent of Wisconsin adults swim. Whether they swim at a pool or in a natural water, common sense precautions can help you maximize your fun. These tips will help you stay safe on the water, avoid getting sunburned and avoid getting sick if there are elevated bacteria levels in the water. Beachgoers can check the DNR's online map to get up-to-date information about water quality at their favorite Great Lakes beaches and at many inland beaches.

Lake Health

How can I get rid of all these weeds by my dock?

Hold on -- that might not be a such good idea! Aquatic plants form the foundation of healthy and flourishing lake ecosystems - both within lakes and rivers and on the shores around them. They not only protect water quality, but produce life-giving oxygen. Aquatic plants are a lake's own filtering system, helping to clarify the water by absorbing nutrients like phosphorus and nitrogen that could stimulate algal blooms. Plant beds stabilize soft lake and river bottoms and reduce shoreline erosion by reducing the effect of waves and current. Healthy native aquatic plant communities help prevent the establishment of invasive non-native plants like Eurasian water-milfoil. They provide important reproductive, food, and cover habitat for fish, invertebrates, and wildlife. So in order to maintain healthy lakes and rivers, we must maintain healthy native aquatic plant communities. Removing any aquatic plants should be done in a manner that limits the disturbance to the overall plant community and may require a permit from DNR. A healthy diversity of native aquatic plants can also help prevent exotic species from becoming established in the lake.

How does a lot of boat traffic affect the water quality of a lake?

Several Wisconsin studies have examined the impact on lakes of boats [PDF]. Generally, the studies found that boat counts on weekends doubled or tripled on average for most weekends; water clarity was temporarily reduced on weekends; shallow lakes and near-shore areas are more affected than deeper lakes; and boat traffic may stimulate algae growth in lakes containing soft-water sediments. Another Wisconsin study concludes that motor boat traffic can reduce aquatic plants by cutting them up or scouring away the sediments they need to grow in. Shoreline erosion from boat wake can also be problematic, especially in small lakes and bays that are protected from wind-generated waves. Much of these impacts can be lessened by operating boats at no-wake speeds in shallow areas. The environmental impact of oil and gas from many of the newer boats with more efficient engines is likely to be minimal versus the older 2-cycle motors; however; the total effects are unknown at this time.

Where can I learn more about the threat of invasive species to Wisconsin's lakes?

Plants or animals that are not native to lakes or streams in Wisconsin are often referred to as "exotic species" and are considered to be "invasive" if the species was introduced by human action to a location, area, or region where it did not previously occur naturally; if it becomes capable of establishing a breeding population in the new location without further intervention by humans; and if it spreads widely throughout the new location. Viral hemorrhagic septicemia, a deadly fish virus found in Lake Michigan and the Lake Winnebago system that can kill a broad range of our native fish, is the latest and potentially most damaging of these unwelcome guests. Invasive species cause more damage in some places than in others, but generally they can crowd out native species, which in turn impacts other species that depend on them for food and habitat, interfere with recreation, impact industry and cost taxpayers and consumers money. The most common way aquatic invasive species are spread to new waters is by clinging to boats, boat trailers, or in bait buckets or bilge water. Cleaning boats before leaving a launch and getting rid of unwanted bait in the trash are key prevention steps. Such prevention is critical because there are no good controls for these invasive species.

Why are pesticides applied to lakes?

Aquatic herbicides are used to reduce the abundance of nuisance-causing plant species, to control the spread of invasive species within and amongst waterbodies, and to improve navigational access to lakes and rivers.  To learn more about how pesticides are used in Wisconsin waters, please go here: Frequently Asked Questions about Aquatic Herbicide Use in Wisconsin.

How can I get involved in protecting my lake?

Wisconsin citizens have a long tradition of protecting the lakes they love, and Wisconsin's regarded as a national model for building a partnership among local citizens, government, and academia to protect lakes. Learn more about the Wisconsin Lakes Partnership and how you can join. Two other great ways you can help: get involved in the Clean Boats, Clean Waters program [exit DNR] and start up, or join in, efforts to educate boaters at landings on how they can prevent spreading invasive species. The Wisconsin Citizen Lake Monitoring Network [exit DNR] trains volunteers how to sample water quality and take other measurements to assess and monitor the health of their favorite lakes.