New York Bay, arm of the Atlantic Ocean at the mouth of the Hudson River, SE N.Y. and NE N.J., enclosed by the shores of NE New Jersey, E Staten Island, S Manhattan, and W Long Island (Brooklyn) and opening on the SE to the Atlantic Ocean between Sandy Hook, N.J., and Rockaway Point, N.Y. It is a sheltered deep harbor able to accommodate the largest ships. The tidal range of the bay is very small and it is ice-free. New York Bay is divided into Upper and Lower Bay, which are connected by the Narrows, a strait (c.3 mi/4.8 km long; 1 mi/1.6 km wide) separating Staten Island from Brooklyn. The Verrazano-Narrows Bridge spans the strait between Fort Wadsworth and Fort Hamilton. Upper Bay, c.5.5 mi (8.8 km) in diameter, is joined to Newark Bay (to the west) by Kill Van Kull and to Long Island Sound by the East River. Historically one of the world's busiest harbors with port facilities on all shores, the New Jersey waterfront is now the most active (see Port Authority of New York and New Jersey). Ellis and Liberty islands (both part of Statue of Liberty National Monument) and Governors Island (site of Fort Jay and Castle Williams) are in Upper Bay. Ferries cross the bay from Staten Island to Manhattan. The larger Lower Bay, which includes Raritan Bay on the west and Gravesend Bay on the northeast is joined to Newark Bay by Arthur Kill. Jamaica Bay is an eastern extension of Lower Bay. Sections of Lower Bay's shoreline are part of Gateway National Recreation Area. Ambrose Channel, federally maintained, crosses Sandy Hook bar at the bay's entrance and extends north to the piers of Upper Bay, where it is 2,000 ft (610 m) wide.