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Water pollutants

Impaired waters in Wisconsin are affected by a variety of pollutants. The top three are: mercury, total phosphorus and sediment. Learn more about these specific pollutants.


Mercury is found in most fish throughout the nation. Fish consumption advice is issued due to mercury and other pollutants that accumulate in fish. In Wisconsin, a statewide advisory applies to all inland waters and exceptions apply to some waters.

Total phosphorus

Phosphorus has long been recognized as the controlling factor in plant and algae growth in Wisconsin lakes and streams. Small increases in phosphorus can fuel substantial increases in aquatic plant and algae growth, which in turn can reduce recreational use, property values and public health.

  • Many lakes and streams are listed as impaired due to phosphorus pollution or sediment, decreasing their recreational value and economic impact.
  • Dozens of waters statewide experience harmful algal blooms fueled by the nutrient, and last year, 35 people in Wisconsin reported human health concerns and the death of at least two dogs due to blue–green algae.
  • Department of Health Services Blue–Green Algae
  • Smelly cladophora fueled by phosphorus washes ashore Lake Michigan beaches.
  • Recent statewide stream assessment data suggests that thousands of streams may have excess phosphorus levels. In addition to decreasing the dissolved oxygen that fish and other aquatic creatures need to survive, such excess phosphorus causes major changes in lake and stream food webs, which ultimately result in fewer fish and fish predators.


Sediment runoff is the loose sand, clay, silt and other soil that settles to the bottom of a waterbody. The most common pollutant in rivers, streams, lakes and reservoirs. When sediment enters a waterbody, it:

  • smothers valuable aquatic breeding ground;
  • damages fish gills;
  • fills in stream channels (which increases the chance of flooding);
  • contributes to the erosion of stream banks;
  • decreases the recreational value of the waterbody; and
  • can be costly for drinking water treatment plants to filter out.

In addition, sediment often carries nutrients with it into Wisconsin streams and lakes.

While natural erosion produces nearly 30 percent of the total sediment in the United States, erosion from human use of land accounts for the remaining 70 percent. In agricultural watersheds, the most significant source of sediment is tilled fields. Farm fields, especially when conventional tilling is used, lack a continuous layer of vegetation to hold the soil in place, so sediment run–off is a major concern. Improperly managed construction sites also contribute significant amounts of sediment to local waterways; up to 25 times that of agricultural lands (Chesters, 1979) and 2,000 times that of forested lands (EPA 833–F–00–008, R 12/2005 [PDF exit DNR]). Construction activities that disturb an acre or more of land are subject to local and state construction site regulations to limit the amount of sediment that is permitted to leave a site. Another significant source of sediment comes from domestic animal activity. Without proper management, livestock can over–graze creating pasture erosion, and trample streambanks.

Last revised: Tuesday May 26 2015