Expanded testing by DC Water found that the Potomac River is healthy and that there is no evidence of lasting harm to the river from January’s collapse of the Potomac Interceptor sewer line.

“We know many in the community, especially people who use the river, have been concerned or had questions,” said DC Water Interim General Manager Matthew T. Brown. “That is why we did more testing. These results are reassuring. They reconfirm what earlier testing indicated - that the river has returned to normal.”

DC Water began testing the river daily shortly after the collapse caused wastewater to overflow into the river. For more than six months, crews collected water samples every day at as many as 10 locations upstream and downstream of the overflow. They tested the samples for E. coli, a type of bacteria commonly used to check water quality. 

Earlier testing showed that bacteria levels had returned to the range normally found in the river. Health advisories were then lifted. In August, DC Water added more testing to get a broader picture of the river’s health. The tests checked oxygen levels, nutrients, and metals, which can affect water quality and impact aquatic life in the river.

DC Water collected samples five times at six locations in Maryland, both upstream and downstream of the overflow. The results were within the normal range for the river. They found no current signs of harm from the overflow.

Results from the expanded testing and months of daily E. coli sampling are available on DC Water’s Potomac Interceptor water quality monitoring page.