Nassau County health officials issued a swimming advisory Tuesday for 11 beaches because of the possibility of elevated bacteria levels.

The advisory is a precautionary measure for beaches known to have substantial storm-water runoff caused by heavy rainfall. The runoff can raise bacteria levels, which result in the waters failing to meet New York State standards for swimming, health officials said.

The Nassau County Department of Health said swimmers should stay out of the water at eight North Shore beaches:

  • Centre Island Sound, Ransom Beach, Soundside Beach and Stehli Beach, all in Bayville;
  • Creek Club in Lattingtown;
  • Laurel Hollow Beach in Laurel Hollow;
  • Piping Rock Beach Club in Locust Valley;
  • Theodore Roosevelt Beach in Oyster Bay.

South Shore beaches included in the advisory are:

  • Hewlett Point Beach in East Rockaway;
  • Island Park Beach in Island Park;
  • Merrick Estates Civic Association in Merrick.

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The agency said the advisory will be lifted at 8 a.m. Wednesday unless there is additional heavy rainfall or water samples reveal elevated bacterial levels.

For recorded information on beach closings and openings in Nassau, call 516-227-9700. Health department representatives are available weekdays from 9 a.m. to 4:45 p.m., at 516-227-9717.