The Outer Barrier, also known as the Long Island and New York City barrier islands, refers to the string of barrier islands that divide the lagoons south of Long Island, New York from the Atlantic Ocean. These islands include Long Beach Barrier Island, Barnum Island, Jones Beach Island, Fire Island and Westhampton Island. The outer barrier extends 75 miles (121 km) along the South Shore of Long Island, from the Rockaway Peninsula in New York City to the east end of Shinnecock Bay in Suffolk County.
The lagoons enclosed by the barrier islands are Jamaica Bay, Brosewere Bay, Hewlett Bay, Reynolds Channel, Middle Bay, East Bay, South Oyster Bay, Great South Bay, and arms of the Great South Bay that have their own geographic names: Great Cove, Nicoll Bay, Patchogue Bay, Bellport Bay, Narrow Bay, Moriches Bay, Quantuck Bay, Tiana Bay, and Shinnecock Bay. East Rockaway Inlet, Jones Inlet, Fire Island Inlet, Old Inlet, Moriches Inlet, and Shinnecock Inlet pierce the barrier, forming the individual sandy islands. The resort communities of Atlantic Beach, Long Beach, and Westhampton Beach; the Fire Island National Seashore, Robert Moses State Park, Jones Beach State Park, and other recreational areas are found there. The low-lying islands are subject to wave erosion, and, during storms, they are sometimes inundated and cut through.