The city Health Department is warning swimmers and kayakers to stay out of the Hudson River after a four-alarm fire shut down a Harlem waste treatment plant Wednesday – causing the city to pump raw sewage into the water, officials said.

“It would take at least 48 hours of continuous discharge before there was any significant impact on water quality for New York City beaches,” said Farrel Sklerov, a spokesman for the Department of Environmental Protection.

If the facility is shut down more than 96 hours, some city beaches may need to be closed, Sklerov said.

“Our guys are going into the building assessing the damage, seeing what has to be done to put the plant back on line,” Sklerov said.

Untreated city sewage is routinely discharged during heavy rains, which dilutes it.

The plant was opened in 1986 and treats up to 170 million gallons of wastewater a day.

“People were running out,” said a plant employee, who declined to give his name. People just wanted to get out.”

Riverbank State Park, which is on the roof of the plant, was evacuated as 168 firefighters worked in 90-plus degree temperatures to control the fire.

The blaze burned for more than three hours, officials said, after fuel under pressure created a 30-foot plume of fire at 11:46a.m. in the engine room of the North River wastewater treatment plant on W.135thSt.

(Source: NY Daily News)