A lagoon's 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's called a lagoon. This application of lagoon in English dates from 1769. It adapted and extended the sense of the Venetian laguna (cf Latin, ‘empty space’), which specifically referred to Venice’s shallow, island-st… (More on Lagoon)