Pollution

Male fish bear eggs in Potomac

Nine male smallmouth bass taken from the Potomac near Sharpsburg, about 60 miles upstream from Washington, were found to have developed eggs inside their sex organs, said Vicki S. Blazer, a scientist overseeing the research for the U.S. Geological Survey.

Note that it says "upstream".

The Potomac River is the main source of drinking water for the Washington metropolitan area and many upstream communities. It provides about 75 percent of the water supply to the 3.6 million residents of Washington and its Maryland and Virginia suburbs.