An island with a central lagoon is called an atoll. Kwajalein in the Indian ocean is a very good example.
staten island
blue lagoon
Each island is surrounded by a reef enclosing a shallow lagoon.
An atoll is a type of island made from a coral reef that encircles a lagoon. It is often the top of an underwater volcano.
atoll
The name of the lagoon in Venice is called the Venetian Lagoon. In Italian, the Venetian Lagoon in called Laguna Veneta.
An encircling coral reef or sandbar can create a shallower area of water near an island, called a lagoon.
A Barrier Reef. The barrier reefs grow parallel to the shore of an island and are separated from it by a deep lagoon.
Poveglia Island is located in the lagoon of Venice, Italy.
barrier reef
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If you are referring to the crossword puzzle hint, try Atoll.