Record-breaking water temperatures at the Potomac River on July 4, 2026, are being linked to a localized fish kill in Maryland. The water temperatures reached a record high of 34.7°C (94.4°F) near Little Falls amid a record-breaking heatwave. Significant fish mortality was reported along a stretch of the river between White’s Ferry and Violette’s Lock soon after.
The District Department of Health lifted a recreational advisory for the Potomac River in Washington, D.C., on March 2, 2026, after three weeks of monitoring showed bacterial levels had returned to typical ranges following the January 19 collapse of the Potomac Interceptor sewer line. Repair operations advanced the following day as crews prepared the damaged pipe for structural reinforcement while environmental restoration continues in the affected section of the C&O Canal National Historical Park.
A section of the Potomac Interceptor sewer line failed on January 19, 2026, in Montgomery County, Maryland, releasing more than 920 million liters (243 million gallons) of untreated wastewater into the Potomac River. By volume, the incident ranks among the largest documented municipal wastewater spills in U.S. history. Elevated bacterial concentrations prompted recreational advisories and shellfish closures while emergency bypass operations continued into mid-February.
