Clear water doesn't necessarily mean it is clean. There are a wide variety of pollutants, both visible and invisible to the naked eye, that pollute our waterways. The federal Clean Water Act requires states to adopt water quality standards to protect lakes, streams, and wetlands from pollution. The standards define how much of a pollutant (bacteria, nutrients, turbidity, mercury, etc.) can be in the water and still meet designated uses, such as drinking water, fishing, and swimming. A water body is “impaired” if it fails to meet one or more water quality standards. The Minnesota Pollution Control Agency (MPCA) is responsible for monitoring and assessing water quality, listing impaired waters, and conducting TMDLs in Minnesota. Monitoring suggests that about 40 percent of Minnesota's lakes and streams are impaired for conventional pollutants, a rate comparable to what other states are finding. All of Rochester's major waterways are considered "impaired." Impaired waters identified through the assessment process are placed on the Minnesota's Impaired Waters List.