Water pollutant


Countless bacteria can be found in land, water, humans, and animals. Most bacteria are beneficial, serving as food for larger organisms and playing critical roles in natural processes such as organic matter decomposition and food digestion. But about 10% of bacteria, such as E. coli, are harmful and, if ingested by humans, can cause sickness or even death.


Bacteria in Minnesota lakes and streams mainly come from sources such as failing septic systems, wastewater treatment plant releases, livestock, and urban stormwater. Waste from pets and wildlife is another, lesser source of bacteria.

Human health and environmental concerns

In addition to bacteria, human and animal waste may contain pathogens such as viruses and protozoa that could be harmful to humans and other animals. The behavior of bacteria and pathogens in the environment is complex. Levels of bacteria and pathogens in a body of water depend not only on their source, but also on weather, current, and water temperature. As these factors fluctuate, the level of bacteria and pathogens in the water may increase or decrease. Some bacteria can survive and grow in the environment while many pathogens tend to die off with time.

Monitoring, reporting, and regulations

Testing for specific disease-producing bacteria or other pathogens is difficult, expensive, and time-consuming. The MPCA tests for fecal coliform and E. coli bacteria, which are commonly found in fecal waste and are easy to measure. They are often used as “indicator organisms” to denote the potential presence of fecal waste. Although using indicator bacteria to assess the presence of pathogens in not a perfect process, it is the best available option at this time. Lakes and streams in Minnesota meet water quality standards if they have a monthly geometric mean less than 126 colony-forming units of E. coli per 100 milliliters of water, between April and October.

Most lakes and streams in Minnesota meet water quality standards for bacteria. MPCA uses the E. coli water quality standard to identify water bodies that may be contaminated with fecal waste. Higher levels of E. coli in the water may or may not be accompanied by higher levels of pathogens and an increased risk of harm; varying survival rates of bacteria make is impossible to definitively state when pathogens are present. See the Minnesota Department of Health Waterborne Illness web page for more information on how to reduce your risk for waterborne illnesses when swimming, boating, or wading.

Is my lake or stream safe for swimming?

Minnesota does not have a list of “safe” bodies of water for recreation. Sometimes a city or county health department will close a swimming beach due to bacterial contamination. Conditions can change over time, and state water-testing efforts are not frequent enough to be time current, particularly in streams and rivers. If you have questions about a specific beach, check with the proper beach authority for their current information and recommendations.

Check with your city or county environmental services to see if your local lake is tested on a regular basis. Two examples of local testing programs:

Addressing bacterial contamination

Some bacteria and pathogens will always be present in surface waters. While most of the bacteria and pathogens from fecal waste in the water will die off over time, some may survive. Pathogens from fecal waste generally die off in the environment much faster than bacteria. While there is not a way to rid water bodies of all pathogens, we can reduce bacteria in surface waters by combining the efforts of many individuals and groups. The best methods include:

  • Controlling runoff on feedlot properties and where manure is spread on farmland
  • Repairing or replacing failing septic systems
  • Improving wastewater treatment processes at some facilities
  • Controlling erosion with practices such as conservation tillage and riparian buffers
  • Rotational livestock grazing, which reduces both sedimentation and fecal coliform concentrations
  • Urban stormwater management – runoff detention, infiltration, and street sweeping

Many government entities and groups across Minnesota are working to better understand sources of bacteria in water and mitigate them. Some examples include:

  • Pollutant reduction studies that lead to limits on bacteria discharged by wastewater treatment facilities to lakes and streams
  • Feedlot runoff controls and other conservation practices installed by farmers because of permit requirements or a statewide water quality certification program
  • County and state programs to bring failing sewer systems into compliance