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Image by CDC
Image by CDC

E-Coli Monitoring

Fecal coliform bacteria (E-Coli) are found in the feces of warm-blooded animals such as people, pets, and wildlife.  E-Coli contamination in streams can come from leaking sewer pipes, pet waste, and wildlife. As the amount of fecal coliform bacteria in the water increases, the risk of contracting a waterborne illness increases.  

E-Coli Results


We test three sites (see map) at Cabin John Creek starting in summer 2023 - Cabin John Local Park, Locust Grove Nature Center, and Goya Drive. We test in warm weather from June to mid-September when bacteria thrive.

E. coli levels up to 410 MPN / 100mL are considered passing based on Maryland and the EPA's water quality single-sample standards for E. coli in surface waters. The science behind that 410 number is really complex, but basically says that if a thousand people recreate in that water, only 36 would get sick! 

  • FAIL (>=410) - High risk so avoid Contact (deemed unsafe by MD State Standards for water play)

  • PASS (<410) - Have fun!


We suggest avoiding contact with creeks 72 hours after a heavy rain. We also recommend keeping your face out of the creek and always hosing down your dog and kids!... or a shower after playing in the creek in the summer. See Montgomery County DEP's bacteria site for more info.

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Our lab work is done by the Anacostia Riverkeeper’s water quality lab.​​

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What do I do?

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During the summer months, E-Coli thrives in warm weather. We are not alone, many places around DC and the Potomac have elevated levels of E-Coli in the summer. Check out TheSwimGuide which we will be posting our data to soon.

If you have a dog, the best thing you can do is pick up the poop! Please pick up after your pet anywhere outside (yard, sidewalk, street, parks, woods) -- you'll be helping Cabin John Creek! Stormwater just flushes it into the storm drains which end up in our creeks.

From DNA testing of water samples, it is estimated that at least 20% of bacteria in waterways comes from dogs. Dog poop has few nutrients yet bacteria love it. Other sources include wildlife and sewer leaks. Check out Montgomery County's site.

Report any sewage leaks to WSSC!


We’ll be testing each summer on every other Wednesday mornings from June through mid-September. 


Want to help? Volunteers can take samples before 9am or drive the samples to Pierce Mill in Rock Creek Park for handoff to the Anacostia Riverkeeper before 10am each Wednesday. We also need volunteers to post results in trail kiosks and our communities. If we get enough volunteers, we can expand to other locations.


Email if you can help on bacteria testing.

Our process documents:

Additional Info

WSSC also performs testing in the Spring and Fall each year as required by their Sanitary Sewer Overflow Consent Decree. Samples are analyzed for human fecal markers and one animal (bird/gull) fecal marker.  In 2022, all human fecal markers were non-detect. WSSC test sites in Cabin John Creek are at MacArthur Boulevard and Cabin John Regional Park. 


Any health alerts or sewage leaks will be posted on the WSSC site or their Sewer Alert Map


Funding for this event provided by: Montgomery County Department of Environmental Protection, Montgomery County Water Quality Protection Fund

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