elongated sandspit, 32 miles (51 km) long and 0.5 mile (1 km) across (at its widest point), Suffolk county, New York, U.S. It lies off the southern shore of Long Island and shelters Great South Bay and part of Moriches Bay from the Atlantic Ocean. The origin of the island's name is unclear. One possibility is that it is a corruption of the Dutch name Vier; another is that the name refers to fires that were built there by pirates to lure ships to the shore. Numerous shipwrecks prompted the building of a lighthouse at the western tip in 1858. Now a popular summer resort, the island is connected to Long Island by two bridges and by passenger ferries.

Robert Moses (formerly Fire Island) State Park, opened in 1908, is on the western end of the island, and Smith Point Park (a county park) covers its eastern section. Most of the rest of the island is now included in Fire Island National Seashore. Established in 1964, the seashore has an area of 30 square miles (78 square km) and includes a number of small communities with year-round residents. No automobile traffic is allowed on the island beyond parking lots at the ends of the two bridges, and most visitors arrive via the ferries. Of particular interest in the national seashore is a 73-acre (30-hectare) “sunken forest,” which is surrounded by sand dunes; when the forest's sassafras, holly, and tupelo trees reach a height of about 35 feet (11 metres), they cease to be protected by the dunes and are sheared off by wind and blowing sand. Other attractions include the lighthouse and the William Floyd Estate, which is on Long Island across Moriches Bay from the eastern end of Fire Island.