If you find yourself with a pesky $30 ticket for for illegally parking in the District of Columbia during street-sweeping hours this year, consider it a donation toward cleaning up the Chesapeake Bay.

D.C. enacted opposite-side-of-the-street parking laws this month as the city gears up for street sweepers to take on the roads of the national capital.

As irritating as it might be for citizens to have to change their parking habits, environmentalists believe the sweepers are doing a public service by helping control toxic runoff into the Chesapeake Bay.

According to WTOP Radio, street sweepers remove 40,000 pounds of oil and grease from District streets every month. That removal leads to a drop of 3,000 pounds of nitrogen and phosphorous runoff per month that usually finds its way into the highly polluted Anacostia and Potomac rivers, which in turn empty into the bay.

So anything the city can do to control runoff, especially to the troubled Anacostia, is seen as a step forward for bay restoration efforts. In addition to runoff from city streets, the District’s shoddy sewer system dumps billions of gallons of raw sewage into the river, and much sediment runs off from the Washington Navy Yard.