Gardiners Bay is a small arm of the Atlantic Ocean, approximately 10 mi (16 km) long and 8 mi (13 km) wide in the U.S. state of New York between the two flukelike peninsulas at the eastern end of Long Island.

The area is fed by the nearby estuaries of Three mile Harbor, Acabonack Creek, and Napeague, which produce ideal environments for shellfish and crustaceans.

Blue claw crab, oysters, and hard shell clams, scallops, and conch are abundant throughout these areas.

It connects by two channels at the north and south end of Shelter Island to Great Peconic Bay.

Gardiners Bay is mentioned in the song 'The Downeaster "Alexa"' by Billy Joel.