DC Water says expanded testing of the Potomac River found no evidence of lasting harm from the January 19, 2026 sewer rupture that released an estimated 240 million gallons of raw sewage into the Potomac River and nearby tributaries over eight days.
Following the collapse of the Potomac Interceptor sewer line, DC Water conducted daily testing for more than six months at as many as 10 locations upstream and downstream of the overflow. Samples were tested for E. coli, with earlier results showing bacteria levels had returned to the range normally found in the river and health advisories subsequently lifted.
In August, DC Water expanded its testing to examine oxygen levels, nutrients and metals to provide a broader assessment of the river’s health. Samples were collected five times at six locations in Maryland upstream and downstream of the overflow.
According to DC Water, the results were within the normal range for the Potomac River and showed no current signs of harm from the sewage spill.
“These results are reassuring,” DC Water Interim General Manager Matthew T. Brown said. “They reconfirm what earlier testing indicated – that the river has returned to normal.”
