The Tappan Zee (; also Tappan Sea or Tappaan Zee) is a natural widening of the Hudson River, about 3 mi (5 km) across at its widest, in southeastern New York in the United States. It stretches about 10 mi (16 km) along the boundary between Rockland and Westchester counties, downstream from Croton Point to Irvington. It derives its name from the Tappan Native American sub-tribe of the Delaware/Lenni Lenape, and the Dutch word zee, meaning a sea or a wide expanse of water.