The Potomac River is cleaner than it has been in decades, earning a “B” grade on the 2025 Potomac River Report Card, the fifth B-level mark in ten years. But “cleaner” doesn’t mean “clean.” Nitrogen, phosphorus, and sediment levels are steadily declining thanks to decades of cleanup work, yet bacterial spikes after rainstorms, persistent chemical contaminants, and a swimming ban in effect for over 50 years tell a more complicated story.
What the River Looks Like Today
The Potomac Conservancy, which issues an annual health assessment, reports that the three biggest pollutants in the river (nitrogen, phosphorus, and sediment) have all been trending downward. More than 20 percent of the watershed’s forest and farmland is now under conservation protection, with over 245,000 acres newly protected in just two years. That land buffer helps filter runoff before it reaches the water.
The picture is less encouraging beneath the surface. Native fish populations are struggling. Smallmouth bass have failed to recover, and striped bass and white perch are declining because of degraded underwater habitat. A river can look clear from the bank and still be in poor biological health, and the fish data suggest the Potomac hasn’t fully turned the corner.
Bacteria Levels and Recreational Safety
The EPA standard for safe recreational contact is 410 E. coli colony-forming units per 100 milliliters of water. On dry-weather days, the Potomac’s D.C. stretch generally meets that threshold. The problem is rain. Washington, D.C. and older surrounding communities use combined sewer systems that carry both stormwater and sewage in the same pipes. During heavy rain, those pipes overflow directly into the river, sending raw or partially treated sewage into the water and causing E. coli levels to spike well above safe limits.
A major infrastructure project, the D.C. Clean Rivers Project, has been building deep tunnels to capture those overflows. The Anacostia tunnel complex, expected to be fully operational in 2025, will nearly eliminate combined sewer overflows into the Anacostia River in an average rainfall year. Similar work along the Potomac side is ongoing but not yet complete. Until it is, bacterial contamination after storms remains a real concern for anyone who paddles, rows, or falls into the water.
Swimming Is Still Banned in D.C.
Swimming has been prohibited in the District’s rivers and streams for over 50 years. The ban dates to August 1971, when the D.C. City Council voted to prohibit water-contact sports in all District water bodies. Multiple layers of federal and local regulations reinforce it. The ban isn’t a relic that officials forgot to lift. The D.C. Department of Energy and Environment can only allow swimming when monitoring proves fecal indicator bacteria concentrations are below specific water quality criteria, verified using EPA-approved testing methods.
There is one exception: permitted Special Swim Events. If monitoring data confirms the water is safe enough on a given day, organizers can apply for a permit and hold a supervised open-water swim. Outside those events, getting in the water remains illegal within D.C. limits. Upstream sections of the Potomac in Virginia and Maryland have different rules depending on jurisdiction, but local advisories still apply after heavy rain.
Chemical Contaminants and Fish Advisories
Beyond bacteria, the Potomac carries chemical pollutants that accumulate in fish tissue over time. Maryland’s Department of the Environment publishes consumption advisories for fish caught in the Potomac, and some of the limits are strict:
- Blue catfish over 30 inches: avoid eating entirely. Smaller ones (12 to 15 inches) are limited to four meals per month.
- Striped bass under 28 inches: up to five meals per month.
- Largemouth and smallmouth bass: three meals per month.
These advisories exist primarily because of PCBs and mercury, industrial chemicals that persist in the environment long after they stop being discharged. Larger, older fish accumulate more of these compounds, which is why the biggest catfish carry the strongest warnings.
A newer concern is PFAS, the group of synthetic chemicals sometimes called “forever chemicals” because they don’t break down naturally. A U.S. Geological Survey study of the Potomac watershed found that while PFAS levels in streams were generally below thresholds harmful to aquatic life, some concentrations approached or exceeded safe limits for drinking water and fish consumption. This is an area where the science is still catching up to the contamination.
How to Check Conditions Before You Go
If you kayak, paddleboard, or row on the Potomac, real-time monitoring data is publicly available. The D.C. Department of Energy and Environment runs monitoring stations along both the Potomac and Anacostia rivers, with sensors taking new readings every 15 minutes. You can access the data through an interactive map on the DOEE website, where clicking on individual stations shows current temperature, dissolved oxygen, pH, depth, and turbidity. The U.S. Geological Survey also publishes real-time water data for the District.
The practical rule of thumb: avoid contact with the water for at least 48 hours after significant rainfall. That window gives bacterial levels time to drop back below the EPA’s recreational safety threshold. On dry stretches, the river is generally safe for boating and incidental contact, though full-body immersion remains both inadvisable and, within D.C., illegal.
The Big Picture
Forty years ago, the Potomac was widely considered one of the most polluted rivers in the country. Billions of dollars in wastewater treatment upgrades, agricultural runoff controls, and land conservation have transformed it into a river that supports recreational boating, sustains bald eagle populations, and provides drinking water to roughly five million people after treatment. The progress is real and measurable. But legacy chemical contamination, rain-driven sewage overflows, and declining native fish populations mean the river is still a work in progress. It’s far cleaner than it used to be, not yet as clean as it needs to be.