Health advisory: Nassau County advises no swimming at 18 beaches due to potential bacteria from stormwater runoff.

Nassau County is warning residents against swimming at 18 beaches on Saturday because of possible elevated bacteria levels, the Nassau County Department of Health announced.

Stormwater runoff caused by rain on Friday could have impacted "bathing water quality by elevating bacteria levels." health officials said in a news release. The county described Saturday’s advisory as a "precautionary measure" targeting beaches that have historically been impacted by stormwater.

The advisory applies to four South Shore beaches — Biltmore Beach Club, Hewlett Point Beach, Island Park Beach and Philip Healey Beach — and 14 on the North Shore: Centre Island Sound, Soundside Beach, Ransom Beach and Stehli Beach in Bayville; Creek Club and Lattingtown Beach in Lattingtown; Morgan Sound and Pryibil Beach in Glen Cove; Laurel Hollow Beach in Laurel Hollow; North Hempstead Beach Park in Port Washington; Piping Rock Beach Club in Locust Valley; Theodore Roosevelt Beach in Oyster Bay; Sea Cliff Village Beach in Sea Cliff; and Tappen Beach in Glenwood Landing.

The advisory will expire at 7 a.m. on Sunday "unless there is additional heavy rainfall or water samples reveal elevated bacterial levels," according to health department release.

Suffolk County’s Department of Health Services could not be reached for comment on whether there are advisories against swimming at any of its beaches.

By Sam Kmack

sam.kmack@newsday.com

Sam Kmack covers the Town of Islip for Newsday. He is a graduate of the University of Southern California and previously worked as a city watchdog reporter in the Phoenix metro area, as well as an investigative journalist at the Arizona Center for Investigative Reporting.