The declaration, rare in scope, was made as million of gallons of untreated sewage were being discharged into the Hudson River from pipes along the length of Manhattan Island.
As New Yorkers reeled from a heat wave, the authorities said that city beaches were still safe to use, but officials worried that a tide of sewage might force some closings unless at least part of the crippled treatment plant could be brought back on line before Friday night.
The prospects for a quick recovery from the fire this week, which started in the main engine room of the North River Wastewater Treatment Plant in Harlem, were uncertain.
“It did significant damage, and we don’t know yet when we will get it back,” said Farrell Sklerov, a spokesman for the city’s Department of Environmental Protection, which operates the treatment plant.
The fire was so severe that a contractor was called in to buttress floors before officials could inspect the damage in the room, which houses five engines. Two of the engines came through the fire in relatively good condition, but they share wiring and fuel lines with the other three.
On Tuesday, just a day before the fire, tests on city waters found them to be in “excellent” condition, with all of them — except the Gowanus Canal — deemed fit for swimming, said John Lipscomb, the manager of water quality sampling programs for Riverkeeper, an environmental advocacy group that monitors conditions in the Hudson.
By Thursday, public boat launches on the Hudson had been shut down. Swimmers young and old were being turned away at the gates of Riverbank State Park, which sits atop the treatment plant, has three swimming pools and other amenities, and was closed because it had no electrical power. People fishing from piers along the river were advised that the water was unsafe.
The city has nearly 600 miles of coastline, and the warning from the health department covers the waters from the Verrazano-Narrows Bridge to the Hudson, Harlem and East Rivers. In those areas, the city says, people should avoid activities that could involve contact with the water. As of Thursday evening, that warning does not apply to the 14 miles of public beaches in the Bronx, Brooklyn and Queens, and on Staten Island. Officials said updates would be posted on the department Web site, www.nyc.gov/health.
New York’s waterways have been transformed over the last four decades, in large part as a result of the city’s 14 sewage treatment plants, which were built or modernized with federal money under the Clean Water Act.
Instead of pouring into rivers and bays, raw sewage is now treated in plants like North River, which is on the Hudson between 137th and 145th Streets and handles waste from the West Side of Manhattan above Bank Street in Greenwich Village. About 120 million gallons a day is treated there, but it can handle up to 340 million gallons when it rains.
The sewage reaches the North River plant from the north and south by gravity flow — running downhill to the plant from the higher elevations of Washington Heights and Inwood, and down an artificial slope from Lower Manhattan. A sewer line about six inches below the street at Bank Street gradually drops to a depth of 50 or 60 feet by the time it reaches the Upper West Side.
At the plant, which is at sea level, the sewage is pumped by engines about five stories up, and as it descends through the plant, the sewage goes through aeration and settling tanks as well as a biological process that digests much of the waste.
It was one of the five pump engines that caught fire on Wednesday, just before noon, officials said. No official cause was declared, but the fire was not considered suspicious. Workers at the plant theorized that a turbocharger on the engine overheated and broke, rupturing a fuel line. That is one of the areas being explored, Mr. Sklerov said.
A warning by the Hudson River near West 90th Street on Thursday. Millions of gallons of untreated waste spilled into the river. (Photo: Monika Graff for The New York Times)
There is no fire suppression system in the engine room, and workers immediately called 911. Four large feeders from Consolidated Edison were shut down.
Firefighters traveled about 400 feet from the entrance to the plant before reaching the machine room, which was belching heavy smoke, said Frank Dwyer, a spokesman for the Fire Department. “The fire was fed by fuel, so they had to put foam on it,” he said. “There was intense heat in there.”
Two firefighters were treated for minor injuries, he said. It took about four hours to bring the fire under control, and by then, no sewage was being treated.
Instead of running to the plant, the sewage was being diverted to 56 “outfalls” — basically, pipes leading directly to the water. They are typically used as a relief system after heavy rain because storm water joins into the sewer lines, and at high volumes can overwhelm the treatment plant. Most of the pipes lead to the Hudson, but a few discharge into the Harlem River.
“This is not a matter of one pipe dumping sewage into the river,” said Philip Musegaas, director of Hudson River programs for Riverkeeper. “This is multiple pipes in a large area.”
The improved condition of the water has brought out a vigorous community of people who take to the water in kayaks and canoes and even as swimmers.
Kathleen Macartney was on the water Wednesday evening, training for a race in an outrigger canoe for two people. Only after she got out of the water did she find out about the sewage crisis. “If I would have known this before, I would not have paddled through the most disgusting water on the planet,” she said.
On Thursday evening, two boys were swimming in the river a short distance from one of the outfalls, and Mr. Lipscomb, who was on the river for more sampling, steered his boat toward shore to warn them. He had no doubt that test results would show that the contamination levels in the river were high. “This is giving us a picture of what it was like four decades ago,” Mr. Lipscomb said. “It’s going to show us how important the money we spent on North River has been to quality of life on the river for humans and other critters.”