A lagoon is a body of comparatively shallow salt or brackish water separated from the deeper sea by a shallow or exposed sandbank, 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. This application 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, (Scotland) and 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.
In Latin America often the use of “laguna”, which lagoon translates to, is used to describe a lake, such as Laguna Catemaco.