Anne Arundel County health officials warned against swimming and urged using caution if fishing in the Patapsco River after 21 million gallons of sewage from Baltimore City recently overflowed into it.

The partially treated wastewater from Baltimore’s Patapsco Wastewater Treatment Plant seeped into the headwaters of the Patapsco River to the mouth of Bodkin Creek, the Anne Arundel County Department of Health announced Friday.

The department was notified of the overflow at 11 p.m. Thursday and issued a weeklong health advisory urging against direct contact with the water. Anne Arundel County beaches are typically under a no-contact, no-swimming advisory for 48 hours after rainfall, but the overflow had extended the warnings.

The Baltimore City Department of Public Works released a statement Saturday confirming the overflow was not a health hazard.

“During a recent rain event, the Patapsco Wastewater Treatment Plant temporarily exceeded its design capacity due to unusually high flows. As a result, a portion of the water being treated skipped the final stage of the process,” a statement from DPW said. “However, the water still went through all the critical steps for removing solids, bacteria, and harmful contaminants — including disinfection before being released. This means the water that was released was not a health hazard. Importantly, recent bacteria testing showed levels well below what is allowed."

The weeklong advisory issued by the Anne Arundel County Health Department was based on early information and has since been corrected, the DPW statement said.

DPW officials do support the general guidance of avoiding open water activities for 48 hours after heavy rain, just to be safe.

The Patapsco River is home to redbreast sunfish, rock bass and smallmouth bass, among other types of fish, according to the Maryland Department of Natural Resources.

Alice Volpitta, Baltimore Harbor waterkeeper for the nonprofit Blue Water Baltimore, said she spoke with an official at Maryland Department of the Environment on Friday who clarified that the discharge from the Patapsco plant is not harmful to human health.

Sewage being processed at the city wastewater treatment plant bypassed a portion of the nutrient removal process, but did not skip any disinfection steps, the environmental official told Volpitta. That means the discharge may have high concentrations of pollutants like nitrogen, which hurt the health of underwater life in the bay, but is not harmful to human health, Volpitta said.

Volpitta said a communication breakdown between the Baltimore Department of Public Works and Anne Arundel County seems to have triggered the health advisory and is “causing everyone to panic.”

“It is a huge problem but it’s not like crisis mode,” Volpitta said.

The Patapsco Wastewater Treatment Plant serves about 450,000 people in Baltimore City and Anne Arundel, Baltimore and Howard counties, according to the Baltimore City Department of Public Works. The facility has enhanced nutrient removal, chlorination and de-chlorination, and is tasked with removing pollutants from incoming wastewater without doing any environmental harm to the Patapsco River and Chesapeake Bay aquatic life.

A 2021 report from Blue Water Baltimore, an environmental nonprofit, found high levels of bacteria in Patapsco Wastewater Treatment Plant’s effluent pipe and revealed that the plant discharged more pollution than what they are permitted to from July 2020–April 2021.

In 2023, Baltimore City was hit with a $4.75 million fine over operations at the Patapsco and Back River wastewater treatment plants and entered a consent decree that required them to hold annual public meetings about progress and replacing and repairing equipment, and submit quarterly reports.

This story has been updated.