Attorney General Brian Frosh (D). (Jonathan Newton/The Washington Post)

The owners of two Maryland power plants in the Washington suburbs will pay $1 million to settle a federal lawsuit alleging illegal releases of nitrogen into rivers, a leading cause of pollution in the Chesapeake Bay.

State Attorney General Brian E. Frosh (D) and Maryland Secretary of the Environment Ben Grumbles on Monday announced the settlement with NRG Energy subsidiaries that own coal-fired generators at the Chalk Point station in Prince George’s County and the Dickerson station in Montgomery County.

The plant operators will pay an additional $1 million to support environmental restoration projects in their watersheds and invest a total of $10 million to upgrade the wastewater filtration systems at the two plants to reduce future pollution.

Maryland filed a lawsuit in 2013 alleging the power plants had discharged wastewater that contained illegal amounts of nitrogen and phosphorus into the Potomac and Patuxent rivers.

Those materials exacerbate the growth of algae blooms that suck oxygen out of swaths of the Chesapeake Bay, making it uninhabitable for fish, crabs and vegetation.

Farms are the biggest source of such pollution, with chemicals in the bay also coming from storm-water runoff, sewage treatment facilities and vehicle emissions.

“The Chesapeake Bay is dying a death of a thousand cuts, or, more appropriately, a million cuts,” Frosh said in an interview. “When someone fails to abide by the law, we will hold them accountable.”

In 2009 and 2010, the plants set up wastewater treatment systems that included pollutant-eating bacteria, which were supposed to minimize the presence of chemicals harmful to the bay.

But the lawsuit filed by the state alleges that those bacteria died shortly after installation of the systems. The lawsuit said that in some years, the Chalk Point facility released 20 times as much nitrogen into the Patuxent River as its permit allows.

NRG Energy is not admitting violations under the settlement.

“It's in the best interests of everyone for us to settle and move on,” said Dave Gaier, an NRG spokesman.

The technology improvements at the plants required under the settlement will augment monitoring for chemical discharges and maximize the treatment of nitrogen.

In 2013, NRG agreed to pay a $1.9 million penalty to settle another lawsuit from the state regarding coal-ash dumps that deposited waste from facilities — including Chalk Point and Dickerson — into landfills.

Power plants have a responsibility to keep Maryland’s rivers, skies, and lands clean for all,” Grumbles said in a statement, later adding in an interview, “This is living proof that we are committed to protecting and restoring the Chesapeake Bay.”

The administration of Gov. Larry Hogan has come under fire from environmental advocates, who say the Republican governor has undermined policies developed with bay restoration in mind.

Last year, Hogan pushed through a repeal of a state mandate for storm-water mediation fees, derided as a “rain tax,” that funded efforts to remove pollutants from rainwater destined for the bay. This month, he announced that he would end a mandate requiring advanced septic systems for individual homes.

Environmental advocates welcomed the settlement with the power plants that was announced Monday but noted that discharges from those plants constitute but a sliver of the pollution plaguing the bay.

For example, nitrogen and phosphorous are also found in common fertilizer, and far greater amounts of those substances enter the bay via runoff from farmland than from the coal-powered generators.

“Ultimately the amount of pollution coming out of those facilities into the bay compared to the [agricultural] industry is not a lot,” said Scott Edwards, an attorney at Food and Water Watch.