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For information on Lakes in Wisconsin, contact:
Wisconsin DNR Lakes
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Bureau of Water Quality

Important Questions and Answers on Wisconsin Lakes

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 find a property that matches that vision. We have several online resources to get you started, particularly if water clarity is one of your priorities. Lakes from Space [exit DNR] 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. Or 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. Finally, 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, consider purchasing from UW-Extension's Lakes program a book about owning waterfront property, Life on the Edge [exit DNR].

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, which are actually photosynthetic bacteria, are largely inedible to other aquatic organisms and as a result, 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.