The Nassau County Department of Health is advising against swimming at 19 beaches because of bacteria concerns.

The agency said Tuesday that swimmers should stay out of the water at 14 North Shore and five South Shore beaches.

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

On the North Shore, 14 beaches are affected:

Centre Island Sound, Bayville; Creek Club, Lattingtown; Lattingtown Beach, Lattingtown; Laurel Hollow Beach, Laurel Hollow; Morgan Sound, Glen Cove; North Hempstead Beach Park, Port Washington; Piping Rock Beach Club, Locust Valley; Pryibil Beach, Glen Cove; Ransom Beach, Bayville; Theodore Roosevelt Beach, Oyster Bay; Sea Cliff Village Beach, Sea Cliff; Soundside Beach, Bayville; Stehli Beach, Bayville; and Tappen Beach, Glenwood Landing.

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On the South Shore, five beaches are affected:

Biltmore Beach Club, Massapequa; Philip Healey Beach, Massapequa; Hewlett Point Beach, East Rockaway; Island Park Beach, Island Park; and Merrick Estates Civic Association, Merrick.

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.