E. Coli. Credit: Getty Images

This story was updated at 7:15 p.m. on Sept. 2, 2022, to include information from WSSC

A nature conservancy group in Bethesda says it is concerned about high levels of E. coli bacteria that it has discovered this summer while testing at various locations of the Willett Branch and Little Falls Branch streams.

The Little Falls Watershed Alliance, a nonprofit started 14 years ago, has been testing levels of E. coli at various points in the streams since 2020. The group is made up of volunteers that have been trained to test the water by the Anacostia Riverkeeper, a nonprofit dedicated to protecting the Anacostia River, alliance Executive Director Sarah Morse told Bethesda Beat on Thursday.

“They provide us with the training, the training manuals, and then we use their lab,” she said.

Morse said her organization started testing the water as a pilot project in 2020. In 2021 and 2022, the group has conducted weekly testing of the two streams for 14 weeks. The alliance chose to do the testing in the summer because it’s the season when children sometimes play in the water.

“The problem with E. coli is that it doesn’t smell and it’s not visible. Kids are playing in there,” she said.

E. coli can cause diarrhea and other types of intestinal illnesses if transmitted through water, food or between animals or people, according to the Centers for Disease Control and Prevention.

The bacteria are measured in MPN (most probable number) per 100 milliliters of water, and anything over 410 MPN/100 ml is considered high, according to the standards used by the Anacostia Riverkeeper, which are based on Maryland and District of Columbia water quality standards.

The alliance has been conducting testing at seven sites and reports that the amount of bacteria found in the water at six sites consistently has been high in recent weeks. The most recent testing was conducted Aug. 31 and the results were:

  • 6,687 MPN/100 ml in Willett Branch at Hillandale Townhomes
  • 2,420 MPN/100 ml in Willett Branch at Norwood Park
  • 2,420 MPN/100 ml in Willett Branch at Morgan Drive
  • 345 MPN/100 ml in Little Falls Branch at Somerset Pool
  • 1,120 MPN/100 ml in Little Falls Branch below Massachusetts Avenue
  • 2,420 MPN/100 ml in Little Falls Branch at the pedestrian bridge and
  • 2,420 MPN/100 ml in Little Falls Branch at Brookmont.

Morse said a representative from the Washington Suburban Sanitary Commission (WSSC) conducted a site visit to Little Falls Branch a few week ago because the utility has a consent decree to monitor that stream.

“According to their testing, there’s no problem,” she said.

Morse said it’s difficult to say why WSSC didn’t find an issue with Little Falls, but noted that some of the testing sites, such as the one in Somerset, have had lower levels of E. coli.

“If you were to test in Somerset, you would pass all the time. But if you go down, not even a mile — we just started testing at River Road — that site fails,” she said.

Luis Maya, a WSSC spokesman, wrote in an email to Bethesda Beat on Friday that the utility is working closely with the Little Falls Watershed Alliance to investigate the cause of the reported high E. coli levels.

“As part of the Sanitary Sewer Overflow Consent Decree, WSSC Water conducts routine water testing in a major stream in all of our sewer basins across Montgomery and Prince George’s counties, which includes Little Falls Branch,” he wrote. “Historic results have shown low levels of human fecal markers in all streams tested, including Little Falls Branch.  Willett Branch flows into Little Falls Branch above the Sanitary Sewer Overflow Consent Decree sample sites.”

So far, WSSC haven’t found any leaks in the area’s sewer mains, but they are continuing to investigate the source of the bacteria, Maya wrote.

Morse said it may come as somewhat of a surprise to the community that children play in the creeks.

“I’ve raised four children and I didn’t think anything of having my children play in the creek,” she said.

Dan Schere can be reached at daniel.schere@bethesdamagazine.com