Bacteria Levels Show Promise but Potomac River Warnings Still in Effect for Washington County

This week’s water‐quality tests at river access points across Washington County reveal that while individual samples were below the single‐sample threshold of 410 MPN, nearly every site continues to exceed the geometric mean limit of 126 MPN for E. coli—with the Potomac River Keeper organization urging caution for swimmers, kayakers and tubers alike. Residents should plan for potential health risks, especially after rain, and follow simple hygiene steps to reduce their chances of illness.

Potomac River Keeper reminds the public that their monitoring focuses solely on the shoreline at boat ramps and parks; test results neither represent deeper river currents nor guarantee safety beyond the moment of sampling. If both the geometric mean and single sample readings register in the red zone, experts classify the risk as “very high,” a concern for children and individuals with weakened immune systems. Sites where the geometric mean is over the limit but the single sample falls below 410 MPN carry a “medium” risk—still calling for vigilance around open wounds and careful handwashing before eating or touching your face.

The organization states that Maryland Department of the Environment (MDE) and EPA guidelines favor using the geometric mean to gauge ongoing water quality, but combine it with single‐sample checks to catch sudden contamination events. A single sample under 410 MPN can offer some reassurance, yet it cannot override an elevated geometric mean built from prior days’ data. With dry conditions, next week’s geometric mean could edge downward—potentially shifting more sites back into the “acceptable” range. Local authorities also emphasize that wet weather drives much of this seasonal spike in bacteria.

No new sewage leaks have been identified in our county, but upstream incidents in Allegany County may continue to influence E. coli counts downstream. However, if individual test bacteria levels remain low next week, warnings may be reduced. Regardless of reported levels, recreators should always treat every river outing as a potential exposure. To protect yourself and loved ones, avoid submerging your head, keep children and pets out of the water after storms, and always rinse off with clean water as soon as possible. For more detailed swimming tips, visit the MDE’s Healthy Beaches page.

Residents can also find up-to-date testing results on the Swim Guide website or app.

Article by multiple contributors, based upon information from Washington County Government Emergency Management and Upper Potomac Riverkeeper monitoring reports

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