A lagoon is a body of shallow sea water or brackish water separated from the sea by some form of barrier.
The body of comparatively shallow salt or brackish water is separated from the deeper sea by a shallow or exposed barrier beach, sandbank of marine origin, coral reef, or similar feature. Thus, the enclosed body of water behind a barrier reef or barrier islands or enclosed by an atoll reef is called a lagoon. When used within this context of a distinctive portion of coral reef ecosystems, the term "lagoon" is synonymous with the term "back reef" or "backreef", which is more commonly used by coral reef scientists to refer to the same area.
These applications of lagoon in English dates from 1769. It adapted and extended the sense of the Venetian laguna (cf Latin lacuna, ‘empty space’), which specifically referred to Venice’s shallow, island-studded stretch of saltwater, protected from the Adriatic by the barrier beaches of the Lido (see Venetian Lagoon). Lagoon refers to both coastal lagoons formed by the build-up of sandbanks or reefs along shallow coastal waters, and the lagoons in atolls, formed by the growth of coral reefs on slowly sinking central islands. Lagoons that are fed by freshwater streams are also called estuaries.
Many lagoons do not include "lagoon" in their common names. Albemarle Sound in North Carolina, Great South Bay, between Long Island and the barrier beaches of Fire Island in New York; Isle of Wight Bay, which separates Ocean City, Maryland from the rest of Worcester County, Maryland; Banana River in Florida; and Lake Illawarra in New South Wales are all lagoons, despite their names. In the UK there are lagoons at Montrose Basin, (Scotland) and Broad Water near Tywyn, (Wales), whilst the expanse of water inside Chesil Beach, England, known as The Fleet, could also be described as a lagoon. There is also one near the small town of Dingle in Western Ireland. Some of the famous lagoons in India are the Chilika Lake in Orissa, near Puri, and the Vembanad Lake in Kerala. Both are connected to the Bay of Bengal and the Arabian Sea respectively through a narrow channel. Some other known lagoons like in Africa, include the Lagos Lagoon which empties itself into the Gulf of Guinea and the South Atlantic Ocean [Keta Lagoon in Ghana.
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