Untreated water was dumped into the Hudson River from 5 p.m. onwards Wednesday, following a fire earlier that day in the engine room at the North River Wastewater Treatment Plant in Harlem.
The Department of Environmental Protection said the plant, located west of the Henry Hudson Parkway from 137th Street to 145th Street, needed to be shut off once it had reached full capacity and stopped treating the wastewater.
Crews were working through Wednesday night to get the plant running again as quickly as possible to once again treat all of Upper Manhattan's sewage.
“That would be what we call a 'bypass.' That would be what would happen when you have a combined sewer overflow when it rains. This would be a dry-weather bypass,” said DEP Commissioner Cas Holloway.
DEP officials said it would take at least 48 hours of continuous discharge of sewage before it would have any impact on city beaches. Yet they would not answer whether kayakers and fisherman should avoid the Hudson River.
The fire at the plant broke out around noon and it took more than 150 firefighters and 40 fire trucks about three hours to get it under control.
Consolidated Edison workers shut off gas to the plant, the facility was evacuated and about 1,000 people were evacuated from Riverbank State Park, located directly above the plant.
"When the units got close enough to see the fire through the smoke, they saw a 30-foot plume of fire that was being under high pressure, exhausted from whatever was leaking," said New York City Fire Department Deputy Assistant Chief Joseph Woznica.
Three firefighters suffered minor injuries, including two cases of heat exhaustion.
The cause of the fire was still under investigation Wednesday night.