Described as a “national disgrace” by Lyndon B. Johnson in the 1960s, a new scientific study indicates that the Potomac  is healthier than it has been in decades.  The study largely attributes the change to upgrades at a District of Columbia sewage plant. The Washington Post reports:

“These conditions are actually better than they were in the 1950s. The portion of the Potomac that we’re talking about was completely devoid of vegetation in the 1950s,” said Nancy Rybicki, a scientist with the U.S. Geological Survey and a co-author of the study.
……
The study covered the period from 1990 to 2007 and 50 miles of river, from Chain Bridge downstream to Maryland Point in Charles County. It was an unusually wide-angle look at the Potomac’s rebound, which has mirrored gains in Boston Harbor and Cleveland’s once-flammable Cuyahoga River.

The Potomac, which begins in Appalachian valleys to the west, once teemed with oysters, sturgeon and shad, but it was poisoned by sewage from the growing capital. By 1969, authorities had pronounced the river “a severe threat to the health of anyone coming into contact with it.”

Its comeback has been closely tied to the Blue Plains treatment plant, which handles waste from the District and parts of Montgomery, Prince George’s, Fairfax, Loudoun and Arlington counties. Its outflow is a river in itself: about 300 million gallons a day of treated sewage, enough to fill RFK Stadium.

In the past decade, responding to mandates from federal regulators, the plant has added $1 billion in new efforts that allow bacteria to consume the algae-feeding pollutant nitrogen in sewage. The new study determined that between 1990 and 2007, the average level of nitrogen in the river fell by nearly half.

The result, scientists said, was less murk. With less algae in the water, more light gets through to the river bottom. Given the chance, the river’s plants came back, the study found: first some nonnative species, then an expanding number of grasses that had always lived in the Potomac. They now cover 8,441 acres of river bottom – and help their own cause by filtering dirt and pollutants out of the current as it passes.

While the overall health of the Potomac has increased drastically, officials continue to discourage individuals from swimming or eating fish from the river as there remain to be unknown chemicals in the water.  Most recently, male bass have been found growing eggs; signifying that the ecosystem remains to have some level of pollution.