A coral atoll.
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Atoll
An island with a central lagoon is called an atoll. Kwajalein in the Indian Ocean is a very good example.
If you are referring to the crossword puzzle hint, try Atoll.
a group of small coral islands in the shape of a ring that encloses a lagoon
An encircling coral reef or sandbar can create a shallower area of water near an island, called a lagoon.
A circular coral reef is called an atoll. Atolls are typically ring-shaped coral reefs that encircle a lagoon partially or completely. They are often found in tropical waters.
Another name for a low-lying island is an atoll. Atolls are circular or oval-shaped coral reef formations that surround a lagoon partially or completely.
Each island is surrounded by a reef enclosing a shallow lagoon.
staten island
A tropical lagoon is encircled by an atoll.
An atoll is a ring-shaped coral reef island that encircles a lagoon partially or completely. Atolls are typically found in the Pacific Ocean and are formed from the remnants of volcanic islands that have submerged over time. The circular shape of atolls is a result of coral growth around the rim of a sinking volcanic island.