Skip to main content

Environmental impacts of agricultural runoff

Agricultural runoff may reduce the water quality in Wisconsin’s lakes, streams and rivers. The same things that help farmers grow healthy crops or raise healthy animals may be too much of a good thing when it comes to water and the life in that water.

Surface water

Too much manure, fertilizers or sediment may pollute lakes, streams and rivers. Improper use or disposal of pesticides, herbicides or medicines (for humans or animals) may also cause water quality problems. Excess nutrients from manure or other agricultural runoff raise the amount of nitrogen or phosphorus in the water. These increases make algae bloom and lower oxygen levels in the water. The increases also make water plants grow too much.

Algae blooms, lower oxygen levels and larger plants hurt the life that lives in our water. It also harms water habitats, ruins the natural beauty and can prevent us from using our lakes, streams and rivers for recreation. The DNR’s Lakes or Rivers and Streams web pages have more information about Wisconsin’s surface water quality.


Many cities and towns, homes, businesses and farms rely on groundwater for clean drinking water. Manure, fertilizers, pesticides, herbicides and pharmaceuticals may pollute groundwater. Once in the groundwater, these pollutants are very difficult to remove.

Nitrogen and bacteria are two of the main pollutants from farms and livestock operations. They can have immediate and severe public health affects in groundwater. Other pollutants such as pesticides, herbicides and pharmaceuticals may have unknown long term health affects. To learn more about public health concerns related to drinking water, your local health department or the Centers for Disease Control and Prevention [exit DNR] have information about drinking water quality.


Wetlands are important water sources for fish and wildlife. They also provide natural flood control and improve water quality. Excessive nutrients and sediment from agriculture and construction (along with improper drainage or filling) change the natural function of wetlands and harm wetland plant communities. Agricultural pollutants, construction and wetlands drainage or filling can lead to habitat losses for plants, animals, fish and birds. The DNR’s Wetlands web pages have additional information about restoring, preserving and protecting Wisconsin’s wetlands.