Waters off the North Shore have been closed to shellfishing for the Fourth of July holiday as a precaution against any increase in sewage discharges from recreational boaters, state officials said.

The ban starts at sunrise on Saturday in the no-discharge zones in Port Jefferson Harbor, Oyster Bay Harbor and the Sand Hole, the Department of Environmental Conservation said, and will be in effect through Wednesday night.

Since 1995, the state has closed these areas for the Fourth and Labor Day holidays because heavier boating traffic could result in more discharges, contaminating nearby shellfish beds, state officials said. Authorities said boaters should use pump-out facilities for sewage to prevent the spread of pathogenic bacteria or viruses that make shellfish unsafe to eat.

The ban covers 445 acres in a section of Oyster Bay Harbor in Oyster Bay Town, 50 acres in the area known as the Sand Hole in Huntington Town and 347 acres in the northern Port Jefferson Harbor in Brookhaven Town.

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If there are fewer holiday boaters due to bad weather, the DEC said, the ban may be lifted before Thursday.

A full list of no-discharge zones in the state can be found at epa.gov/region2/water/ndz/.