WASHINGTON, D.C. — A nonprofit group says authorities in the United States capital Washington have failed to properly warn the public about a massive sewage leak into the Potomac River, thought to be among the largest such spills in the nation’s history.

A 6-foot-wide rupture in an aging line on Jan. 19 released 40 million gallons of raw effluent until Jan. 24, when DC Water, the city’s water utility, activated a bypass that channeled the flow through a canal and back into another section of the line.

Overflow is still entering the river, albeit at a reduced rate, as workers try to plug the gap — efforts that have been hampered by subzero temperatures and one of the worst snowstorms in years, which has yet to be fully cleared days after it passed.

Dean Naujoks of the nonprofit Potomac Riverkeeper Network said that while it was clear that authorities were doing their best to contain the spill, they had failed to adequately convey public-health risks to the public.

“I’ve dealt with a lot of sewage spills, but this is definitely the largest I’ve ever dealt with,” he told Agence France-Presse (AFP), adding that his organization estimated that 300 million gallons had now entered the river.

That figure is equivalent to around 450 Olympic-sized swimming pools and higher than a reported 230-million-gallon spill along the US-Mexico border in 2017.

Sampling by the group found levels of E. coli bacteria at 12,000 times higher than limits set by authorities for human contact, Naujoks said, adding that he returned to the rupture site again on Wednesday to test for other contaminants.

E. coli is a type of bacteria that resides in mammal guts and is considered a proxy indicator for water quality and pollution levels.

“It’s really concerning and yet, we’re the only ones doing the sampling,” he added.

Public-health agencies typically issue advisories in summer, when people are more likely to recreate in the water, including paddling and fishing. So far, the state of Maryland has activated a shellfish consumption advisory, but the District of Columbia has not taken similar steps