The Great South Bay is a lagoon  situated between Long Island and Fire Island, in the State of New York. It is about 45 miles (72 km) long and has an average depth of 4 feet 3 inches (1.3 m) and is 20 feet (6.1 m) at its deepest.  It is protected from the Atlantic Ocean by Fire Island, a barrier island, as well as the eastern end of Jones Beach Island and Captree Island.
Robert Moses Causeway adjoins the Great South Bay Bridge, which leads to Robert Moses State Park.
The bay is accessible from the ocean through Fire Island Inlet, which lies between the western tip of Fire Island and the eastern tip of Jones Beach Island. The bay adjoins South Oyster Bay on its western end, and Patchogue and Moriches bays at the east end.
In the early 17th century, European settlers first encountered the native Montaukett Indian Nation. Among the earliest British families were the Smith, Carman and Hewlett families.  Long Island's South Shore, which includes Lindenhurst, Babylon, Islip, Oakdale, Sayville, Bayport, Blue Point, Patchogue, Bellport, Shirley, and Mastic Beach.
In the late nineteenth century Great South Bay provided many of the clams consumed throughout the region and even the country. The first oysters to be exported from the US to Europe came from Great South Bay. By the latter 20th century, a significant percentage of the habitat was lost.  Hurricane Sandy, the largest storm to affect the region since 1938, made landfall with devastating impact to Fire Island sea shores, including multiple breaches, the largest of which formed just south of Bellport. This was formerly known as Old Inlet. Residents were concerned it would have effects on tidal increases and potential flooding, when in actuality it has allowed the bay to relieve some of its captive water, which has changed the salinity and nitrogen levels in the bay.  After roughly 75 years, the bay begun flushing itself out which may improve the water condition within the bay.  Regulations set forth by the US Government National Wildlife Preserve, which has a seven-mile stretch of land (The Otis Pike Fire Island High Dune Wilderness) prohibit any unauthorized parties from performing any kind of man made changes, thus the inlet has remained open. There have been a number of ongoing public meeting discussing the future of the Inlet.  All the other breaches were closed by the Army Corps of Engineers. In 2012, The Save the Great South Bay (STGSB) not-for-profit organization was formed in order to work towards better conservation of the water and its beachfronts.   Save The Great South Bay has increased concerns about boat sewerage pumpouts in The Great South Bay as a serious ecological concern. 
Bellport is a village in the Town of Brookhaven in Suffolk County, on the South Shore of Long Island, in New York, United States. The population was 2,084 at the 2010 census.
East Patchogue is a census-designated place (CDP) in the Town of Brookhaven in Suffolk County, on the South Shore of Long Island, in New York, United States. The population was 22,469 at the 2010 census. The CDP is a proximate representation of the East Patchogue hamlet used for statistical purposes of the Census Bureau.
Long Island Sound is a marine sound and tidal estuary of the Atlantic Ocean. It lies predominantly between the U.S. state of Connecticut to the north and Long Island in New York to the south. From west to east, the sound stretches 110 mi (180 km) from the East River in New York City, along the North Shore of Long Island, to Block Island Sound. A mix of freshwater from tributaries and saltwater from the ocean, Long Island Sound is 21 mi (34 km) at its widest point and varies in depth from 65 to 230 feet.
Jamaica Bay is an estuary on the southern portion of the western tip of Long Island, in the U.S. state of New York. The estuary is partially man-made, and partially natural. The bay connects with Lower New York Bay to the west, through Rockaway Inlet, and is the westernmost of the coastal lagoons on the south shore of Long Island. Politically, it is primarily divided between the boroughs of Brooklyn and Queens in New York City, with a small part touching Nassau County.
The Town of Brookhaven is the most populous of the ten towns of Suffolk County, New York, United States. Part of the New York metropolitan area, it is located approximately 50 miles from Manhattan. It is the largest of the state of New York's 932 towns by area, and the second most populous after the Town of Hempstead.
South Oyster Bay or East Bay is a lagoon and natural harbor along the western portion of the south shore of Long Island in New York in the United States. The harbor is formed by Jones Beach Island, a barrier island on the southern side of Long Island. It is approximately 3 mi (5 km) wide between the two islands, and approximately 15 mi (24 km) long. It links to Great South Bay on its eastern end and opens to the Atlantic Ocean through inlets on either side of Jones Beach Island.
Fire Island is the large center island of the outer barrier islands parallel to the South Shore of Long Island, in the U.S. state of New York.
Fire Island National Seashore (FINS) is a United States National Seashore that protects a 26-mile (42 km) section of Fire Island, an approximately 30-mile (48 km) long and 0.5-mile (0.80 km) wide barrier island separated from Long Island by the Great South Bay. The island is part of New York State's Suffolk County and the Outer Barrier.
Montauk Highway is an east–west road extending for 95 miles (153 km) across the southern shore of Long Island in Suffolk County, New York, in the United States. It extends from the Nassau County line in Amityville, where it connects to Merrick Road, to Montauk Point State Park at the very eastern end of Long Island in Montauk. The highway is known by several designations along its routing, primarily New York State Route 27A (NY 27A) from the county line to Oakdale and NY 27 east of Southampton. The portion of Montauk Highway between Oakdale and Southampton is mostly county-maintained as County Route 80 and County Route 85.
Smith Point County Park is a beachfront park facing the Atlantic Ocean on the east end of Fire Island, along the central south shore of Long Island, near Shirley, New York, United States. It is the largest park owned by Suffolk County.
The South Shore of Long Island, in the U.S. state of New York, is the area along Long Island's Atlantic Ocean shoreline.
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.
Patchogue Bay is a lagoon on the south-central shores of Long Island in the U.S. state of New York.
The Swan River is in Suffolk County on Long Island, New York. It flows into Swan Lake from the north, and then south out of the lake into the mouth of Patchogue Bay, which then becomes the Great South Bay. Originally, the headwaters reached as far north as Medford, New York, near the vicinity of the Long Island Rail Road's Medford station. Swan River is a relatively clean, cold, free flowing, freshwater stream, generally less than 15 feet wide, with a sandy substrate. This segment of the river flows through much undeveloped forested wetland, but has also been encroached upon by residential development, road construction, and a commercial sand mining operation. Below Montauk Highway, the river is tidal, and is bordered by undeveloped marshland and limited development of boat docking facilities. The fish and wildlife habitat encompasses the entire river, including an approximate one and one-half mile tidal segment, and an approximate two and one-half mile freshwater segment, which extends from Swan Lake, above Montauk Highway, to the headwaters of the stream, above Swan Lake, flowing southward into Patchogue Bay.
The South Shore Estuary is an estuary located along the south shore of Long Island, between the mainland and the outer barrier islands, in eastern New York state. It stretches for over 70 miles (110 km) from West Bay in Nassau County to the Shinnecock Bay in Suffolk County.
Cupsogue Beach County Park is a 296-acre (1.20 km2) park at the eastern end of Fire Island and the western end of Westhampton Island, known locally as Dune Road, one of Long Island's easternmost barrier islands. The park is surrounded by the Atlantic Ocean, Moriches Inlet and Moriches Bay.
Moriches Bay is a lagoon system on the south shore of Long Island, New York. The name Moriches comes from Meritces, a Native American who owned land on Moriches Neck.
The Smith Point Bridge is a steel bascule drawbridge in Shirley, New York that connects Long Island to Fire Island. Located on the south shore of central Suffolk County, the bridge carries William Floyd Parkway across The Narrows between Bellport Bay and Moriches Bay. It connects Long Island with Smith Point County Park and the Otis Pike Fire Island High Dune Wilderness, both are a part of the Fire Island National Seashore.
Coordinates: 40°41′25″N73°06′07″W / 40.69028°N 73.10194°W