WOODBURY - The Nassau County Department of Health has closed 19 beaches to bathing as a precautionary measure following heavy rainfall.Officials say storm water runoff can have a negative impact on water quality by elevating bacterial levels.The following 14 Nassau County North Shore beaches are closed, effective today: Centre Island Sound, Creek Club, Lattingtown Beach, Laurel Hollow Beach, Morgan Sound, North Hempstead Beach Park, Piping Rock Beach Club, Prybil Beach, Ransom Beach, Roosevelt Beach, Sea Cliff Village Beach, Soundside Beach, Stehli Beach and Tappen Beach.The following 14 Nassau County South Shore beaches are closed, effective today: Biltmore Beach Club, Hewlett Point Beach, Island Park Beach, Merrick Estates Civic Association and Philip Healey Beach.