How does the city decide if beaches are clean enough to open?

For some New Yorkers, the official opening of the city’s beaches is the most anticipated part of Memorial Day Weekend. But the miles of sandy surf can’t always be taken for granted. Shutdowns for pollution are a regular feature of urban beachgoing, like last year, when at the height of summer a fire at a Manhattan waste treatment plant spilled raw sewage into the Hudson River.

But many reasons for shutdowns are less odorous or obvious. No one thinks New York City’s waters are pristine. But how dirty is too dirty? Today’s Daily Q asks: How does the city decide that a public beach is clean enough for swimming? 

What we found

New York City’s beaches are swimming with bacteria and other pollutants, so they have to pass a few tests before city officials deem them safe for urban sunbathers. Some are common-sense — like checking to see if lifeguards have spotted anything strange in the water — but the most important are the results of weekly water samples that the city’s Department of Health collects from the city’s public and private beaches.

Staff from the health department’s Bureau of Public Health Engineering test for the presence of bacteria called enterococci, which is most commonly found in human waste. The tests begin in April, about a month before the kickoff of beach season, and continue until September. Testers collect at least three samples of water at each location, in which enterococci cannot exceed 104 colonies per milliliter. Federal standards forbid human bathing once bacteria surpass these levels.

To put that into perspective, if you were to empty a 1 liter bottle of soda and fill it with water from your favorite beach, you could expect to find just over 1,000 colonies of enterococci in there. Don’t drink it (seriously, don’t), but feel free to swim in it.

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