Blue Water Baltimore filed a lawsuit against Baltimore City on Wednesday, demanding it fix problems at its two sewage treatment plants that have sent massive amounts of bacteria and pollution into the Chesapeake Bay for more than a year.

The water quality advocacy group revealed in August that the city’s Patapsco and Back River wastewater treatment plants sent millions of gallons of partially treated sewage into waterways every day for months. A state inspector found that problems began a year earlier, in August 2020.

The lawsuit, filed in U.S. District Court for the District of Maryland under the federal Clean Water Act, seeks to have a judge order the city to stop the pollution and, potentially, pay a fine.

Alice Volpitta, the Baltimore Harbor Waterkeeper, said Blue Water Baltimore has been working with the city Department of Public Works and the Maryland Department of the Environment as they develop a plan for the city to correct problems at the plants. The lawsuit seeks to ensure that work continues, should such an intervention by the court become necessary, she said.

“This is about making sure that we’re keeping all avenues open,” Volpitta said. “It’s making sure the people who are already paying the price for these violations have a voice moving forward about how we’re protecting water quality.”

Baltimore Public Works officials declined to comment and referred a reporter to the city law department. An official there could not be reached Wednesday.

The revelation of the plants’ pollution has raised alarm among Chesapeake Bay advocates because it shattered their belief that the facilities actually had significantly reduced their impact on waterways in recent years. Many of them criticized state regulators for not monitoring the plants more closely or detecting the problems earlier.

Blue Water Baltimore, a nonprofit that houses the Baltimore Harbor Waterkeeper program, only learned of the pollution through its own routine monitoring of waterways, which showed high levels of fecal bacteria, nitrogen and phosphorus around one of the plants.

The state Department of the Environment said it became aware of the problems in late 2020; however, it did not alert the public to the unsafe levels of bacteria or the large amounts of nutrients coming from the plants until Blue Water issued a press release of its own.