An alert against swimming and bathing at 63 beaches has been issued by Suffolk County because levels of bacteria may have risen due to this week's heavy rain.

The beaches covered by the advisory are on the North and South shores, in areas that are often inundated by storm water runoff from nearby watersheds or tributaries, or have limited tidal flushing, the Suffolk County health department said.

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The advisory affects bay beaches and Long Island Sound beaches, including Lake Ronkonkoma-Islip Town Beach, Amityville Village Beach, Shoreham Beach, Asharoken Beach, Crab Meadow Beach in Northport, Islip Beach and Shirley Beach.

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Health officials suggest not even touching the water until the rain has stopped and at least 24 hours has passed.

The advisory will be lifted Thursday morning unless elevated levels of bacteria are found in water samples, health officials said.

Information on the beaches affected and updates on the beach monitoring program are at suffolkcountyny.gov/Departments/HealthServices/EnvironmentalQuality/Ecology/BeachMonitoringProgram.aspx . Also for details, call the bathing beach hotline at 631-852-5822 or the health department's ecology office at 631-852-5760.