Potomac Interceptor collapse among largest municipal wastewater spills in U.S. history

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. Source