On January 19, 2026, a section of the 72-inch-diameter Potomac Interceptor (PI) sewer line collapsed near the Clara Barton Parkway in Montgomery County, Maryland, which is approximately upstream of Washington, D.C. An estimated 240 million to 300 million gallons of untreated wastewater was spilled into the Potomac River. According to the University of Maryland School of Public Health, the sewage spill is one of the largest in U.S. history.
The Potomac Interceptor sewer, principally constructed in 1962, originates in the Virginia and Maryland suburbs, and transports wastewater from Dulles International Airport, surrounding communities in Virginia, and parts of Montgomery County to the Blue Plains Advanced Wastewater Treatment Plant in Washington, which is owned by District of Columbia Water and Sewer Authority (DC Water). This large piping system is constructed of reinforced concrete pipe, and one section of the system is located within the Chesapeake and Ohio Canal National Historical Park. DC Water is responsible for managing most of the PI sewer infrastructure. The Washington Suburban Sanitary Commission (WSSC) manages a section of the PI in the Maryland suburbs.
DC Water installed a bypass system in cooperation with the National Park Service (NPS) that diverts sewage upstream of the collapse into a dry stretch of the C&O canal and carries the wastewater 2,700 feet before the water enters a non-damaged part of the Potomac Interceptor downstream. The canal was dammed at lock 14 to prevent snowmelt from entering the bypass section and wastewater returned to the PI near lock 10
DC Water activated the bypass on the evening of January 24th and started capturing the majority of the wastewater. Later, the bypass was enhanced with additional pumps bringing water into the canal to add capacity and redundancy.
Video inspection of the PI showed significant blockage inside the collapsed sewer line including a large rock dam about 30 feet beyond the initial collapse location. Crews were able to reach the damaged pipe section by February 19, once a steel bulkhead gate was installed to block sewage from entering it.
On February 16, 2026, President Donald Trump announced that the federal government will respond to the spill, while blaming Democratic leaders of local authorities, particularly Maryland Governor Wes Moore. A spokesman for Moore stated that, "The President has his facts wrong â again," explaining that the Trump administration is "actually supposed to be in charge here." The Maryland Department of the Environment (MDE) does not regulate DC Water, but is monitoring water quality in the river. DC Water has been managing the PI repairs and is issuing daily updates. The District of Columbia Department of Energy and Environment is issuing weekly updates about the PI, pertaining to water quality monitoring and related information.
DC Water has estimated the repair and remediation costs to be $20 million. On February 18 Mayor Muriel Bowser of Washington declared a public emergency. Bowser requested federal assistance and reimbursement, and a presidential disaster declaration. On February 19 Trump announced that the federal government is responding to Bowser's request, with the U.S. Environmental Protection Agency (EPA) leading the response, along with the Federal Emergency Management Agency. The US Army Corps of Engineers began providing assistance at the spill site on February 21.
On March 14, the emergency repair efforts were completed. The water is now directed via the interceptor. All bypass pumps were turned off. New long-term work is being done to rehabilitate and strengthen the pipe, which is expected to take 9-10 months.
The wastewater had a significant impact on the bacteria levels in the Potomac. E. coli bacteria levels were hundreds of times higher than the EPA's safety levels when the water was tested. Because the river was frozen over, downstream water in Georgetown was within safety limits published by the U.S. Environmental Protection Agency (EPA).
The Maryland Department of the Environment (MDE) has stated that "All active Maryland drinking water intakes are upstream and unaffected." On January 25 the agency closed one downstream shellfish harvesting area in Charles County as a precautionary measure. MDE has conducted several inspections at the spill site jointly with EPA. Three Maryland counties (Montgomery, Prince George's and Charles County) have issued health advisories recommending avoiding recreational activity in the river.
On February 17, the government of Arlington County, Virginia, released an announcement that the county's drinking water was safe for human consumption. The same announcement repeated the advice of the Virginia Department of Health, which had issued a recreational activity advisory encouraging people to avoid being in the Potomac due to concerns regarding the spread of illness.
The drinking water systems in Maryland and Washington are also not affected by the spill. The principal drinking water intake for Washington and Arlington is located upstream of the spill at Great Falls. While a smaller, supplemental intake for the Washington Aqueduct system is located at Little Falls, downstream of the spill, it had been shut off before the January spill. The Potomac River water intake for the Montgomery County system, operated by WSSC, is also located upstream of the spill.