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E. coli in Surface Waters

WRD Biologist sampling E. coli
Environment, Great Lakes, and Energy

E. coli in Surface Waters

Contact: Molly Rippke 517-342-4419 

Download Michigan's E. Coli Water Quality Standard Guidance

View the E. coli EnviroMINUTE video

What is E. coli?

Escherichia coli (E. coli) is a type of bacteria (single cell organism) that is used by the State of Michigan as a water quality indicator. When E. coli is found in surface waters, it means that there has been fecal contamination. While E. coli itself may be harmful to human health, other disease-causing organisms might also be present. Once these pathogens are in a stream or lake, they can infect humans through ingestion or skin contact, resulting in diseases such as gastroenteritis (diarrhea), giardia, hepatitis, or cholera.

How does E. coli get into surface water?

Common and potential sources of E. coli contamination vary by where you are in the landscape. For example, urban areas would be expected to have a different set of sources than a rural farm-type setting where there are livestock and people rely on septic systems. All animals (livestock, pets and wildlife) and human sewage are possible sources under certain circumstances. For more details on sources and how EGLE works to prevent them from entering surface water, see Michigan's Statewide E. coli TMDL.

To find out how you can help reduce E. coli contamination of our rivers, lakes, and beaches, please see our Guide for Homeowners.

How much E. coli is too much?

The Water Quality Standard for E. coli was developed to protect human health during work and play, and is the maximum amount of E. coli that is allowable in surface waters of the state. These standards, known as the total and partial body contact (or recreation) standards, apply to all waters of the state, including streams, rivers, wetlands, lakes and beaches. The geometric mean of three samples at the site (collected on the same date) are needed to compare to the standard as described by Rule 62 of the Part 4 Water Quality Standards. The water quality standard is more conservative during the summer to protect swimmers during total body contact, but water is protected all year round by the partial body contact standard. For a 30-day geometric mean calculation, five weekly sampling events are needed, within a 30-day period.

Water Quality Standard for E. coli:

Total Body Contact (May 1 - October 31):
Daily Maximum Geometric Mean: 300 E. coli per 100 milliliters (ml)
30-Day Geometric Mean: 130 E. coli per 100 ml

Partial Body Contact (all year):
Daily Maximum Geometric Mean: 1,000 E. coli per 100 ml

How is E. coli measured?

E. coli in water exists in colonies that can be suspended in the water, or settle out with gravity. E. coli water samples should be collected in a manner that does not disturb the bottom sediment, and avoids capturing surface films or scums. Sterile containers and gloved hands are used to minimize sample contamination. Samples are collected from three locations (generally called 'left", "center" and "right") at each site of interest, such as a road crossing of a river or a bathing beach. Samples should be taken to a laboratory within 6 hours, to prevent regrowth or death of the bacteria. Once at the lab, the personnel will count the colonies using one of several methods and report the results in colonies per volume of water. Then, a geometric mean of these three samples is calculated to compare with the water quality standard. For a 30-day geometric mean calculation, five weekly sampling events are needed, within a 30-day period.

What resources can I access to help me sample my waterbody?

Example map from Ecoli mapper

Where can I find E. coli data?

What does EGLE do when we find a problem?

When the water quality standard is exceeded at a beach, lake or stream, EGLE goes through a process that is defined by the Federal Clean Water Act Section 303(d). Simply put, the state must make a list of all waters that are not meeting the standards or designated uses, then must address the issue in a document called a Total Maximum Daily Load. The state of Michigan estimates that roughly half of its rivers and streams exceed the Total Body Contact E. coli standard. Dozens of TMDLs have been U.S. EPA approved to address E. coli issues at beaches and on rivers, lakes and streams in Michigan. However, a TMDL itself does not make water clean, it is only a step in a long process which requires cooperation and efforts of multiple agencies (state and local) and public participation to be successful.

TMDL Watershed Screening Tool (Interactive Map)