Bacteria are natural and can be found in land, water, as well as in and on 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 some are harmful and, if ingested by humans, can cause sickness or even death.

The majority of concern when it comes to bacteria in streams and lakes is when the bacteria source is from a human or animal. Common sources of bacteria that can be of concern are failing septic systems, wastewater treatment plant releases, livestock, urban stormwater, pets, and wildlife. 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 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.

Bacteria and Water Monitoring

Testing for specific disease-producing bacteria or other pathogens (viruses, protozoa, etc.) is difficult, expensive, and time-consuming. Different organizations in Missouri test for fecal coliform and E. coli bacteria, which are commonly found in fecal waste and are easy to measure. Both of these bacteria are used as “indicator organisms” that indicate the presence of fecal waste is likely. While not a direct measure of other pathogens, use of indicator bacteria to assess the presence of pathogens is the most cost effective and timely way.

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 it impossible to definitively state when what pathogens are present.

Is my lake or stream safe for swimming?

The department samples water quality at all designated swimming beaches in the state park system on a weekly basis during the recreational season. The samples are analyzed at the Environmental Services Program laboratory in Jefferson City, and results are posted on the department's beaches webpage.

Water sample results can help visitors decide whether a particular beach is suitable for swimming, based on the bacteria levels. In accordance with state law, the Missouri Department of Natural Resources will post signs notifying visitors that swimming is not recommended if the geometric mean of the weekly water quality sample results exceeds the equivalent of 190 E. coli colonies per 100 milliliters of water (190 mpn/100 ml).

Some county health departments also test popular recreation areas for E.coli. Check with your local health department for more information.

Additional information on recreation in surface waters can be found in the Missouri Department of Health and Senior Services Swim Healthy Stay Healthy brochure.

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 isn’t 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.

  • Repairing or replacing failing septic systems
  • Check with your local Soil and Water Conservation District
    • Controlling runoff on feedlot properties and where manure is spread on farmland
    • Controlling erosion with practices, such as conservation tillage and riparian buffers
    • 319 Watershed Management Plans
  • Urban stormwater management – runoff detention, infiltration, clean-up of pet wastes