Nassau County Health Department officials Sunday issued an advisory against bathing at 19 beaches where they said bacteria levels may be elevated due to storm-water runoff caused by heavy rainfall.

The advisory was expected to be lifted Monday morning if there is not another heavy rain.

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"This occurs frequently when we have a half-inch of rain in a 24-hour period," health department spokeswoman Mary Ellen Laurain said. "This advisory is issued as a precautionary measure for beaches known to be impacted by storm-water runoff caused by heavy rainfall."

Laurain said storm-water runoff can affect bathing water quality by pushing bacteria levels beyond the acceptable New York State standard.

Beaches named in the advisory: Centre Island Sound and Theodore Roosevelt Beach, Oyster Bay; Creek Club and Lattingtown Beach, Lattingtown; Laurel Hollow Beach, Laurel Hollow; Morgan Sound and Pryibil Beach, Glen Cove; North Hempstead Beach Park, Port Washington; Piping Rock Beach Club, Locust Valley; Ransom Beach and Soundside Beach, Bayville; Sea Cliff Village Beach and Tappen Beach, Sea Cliff; Stehli Beach, Locust Valley, Biltmore Beach Club and Philip B. Healey Beach, Massapequa; Hewlett Point Beach, East Rockaway; Island Park Beach, Island Park; and Merrick Estates Civic Association, Merrick.