Concerns over bacteria closed 19 Nassau County beaches, health officials said Wednesday.

The beaches are closed to swimming as a precautionary measure, the Nassau County Department of Health said, citing recent heavy rains.

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Stormwater runoff can sweep bacteria and pathogens into streams and bays, causing bacterial levels to spike, according to health officials.

Fourteen closed beaches are on the North Shore: Centre Island Sound, Creek Club, Lattingtown Beach, Laurel Hollow Beach, Morgan Sound, North Hempstead Beach Park, Piping Rock Beach Club, Pryibil Beach, Ransom Beach, Roosevelt Beach, Sea Cliff Village Beach, Soundside Beach, Stehli Beach and Tappen Beach.

Five are on the South Shore including: Biltmore Beach Club, Hewlett Point Beach, Island Park Beach, Merrick Estates Civic Association and Philip Healey Beach.

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.