Read our Privacy noticeA toxic plume of contamination is sweeping down the Potomac River after a massive sewage‑pipe failure sent hundreds of millions of gallons of waste into the waterway, a report says. Testing by the Potomac Riverkeepers shows the scale of the contamination. Four miles downstream, at Fletcher’s Boathouse in D.C., levels were still 60 times higher than what is considered safe. open image in gallery Water samples are taken by workers on the sewage-blighted Potomac River ( AP )“We found alarmingly high numbers of sewage E. coli in the river,” said Naujoks. DC Water advised anyone exposed to the water to thoroughly wash their skin.