Upper Potomac Bacteria Levels Return to Safe Limits, One Antietam Creek Site Exceeds Threshold

According to Upper Potomac Riverkeeper, the latest shoreline tests from July 23 show that 13 of 14 monitored sites for the Upper Potomac River area remained below the state’s 410 MPN single-sample limit for bacteria, offering reassurance to local swimmers and anglers. Only the Security Road access point on the Antietam Creek registered a high 579.4 MPN, prompting a fail designation and a renewed call for caution at that location.

Earlier in July, concerns mounted when routine monitoring revealed that average E. coli levels across several Upper Potomac sites were exceeding the recommended geometric mean of 126 MPN, even if individual samples rarely surpassed the 410 MPN single-sample threshold. Those findings reignited worries about potential sewage contamination from May’s flood-damaged systems, prompting the Maryland Department of the Environment to inspect sewer infrastructure and collect extra samples. Although MDE ultimately determined that flood-related leaks were not the primary cause, swimmers and riverfront communities remained on alert as higher temperatures and sporadic storms continued to drive bacterial growth and occasional spikes in readings.

Aside from Security Road on the Antietam Creek, popular spots including Williamsport Park (198 MPN), Big Slackwater Boat Ramp (27.5 MPN), and Riverside Park (275.5 MPN) all passed this week’s screening. Sites in Washington County, MD—such as Brunswick Campground (35.9 MPN) and Funkstown VFD (124.6 MPN)—also recorded low readings, as did Maryland locations like Burnside Bridge (129.6 MPN) and Buckeystown Park (39.3 MPN). West Virginia’s Snyders Landing (41 MPN) and Shepherdstown (16.1 MPN) likewise reported minimal bacterial presence.

Despite the largely positive results, the failure at Security Road underscores the lingering impacts of summer storms, which can wash urban and agricultural runoff into the river. State guidance still recommends avoiding swimming for at least 48 hours after heavy rain, steering clear of cloudy or discolored water, and keeping pets out of the river post-storm to limit exposure to harmful bacteria.

Residents planning river outings should check the Swim Guide app or Potomac Riverkeeper Network social media for the most up-to-date results before entering the water. To reduce health risks, avoid sites with known discharge points, cover any cuts with waterproof bandages, and always shower and wash hands thoroughly after water contact.

Article by multiple contributors, based upon information from Upper Potomac Riverkeeper monitoring reports

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