<P> A cay (/ ˈkiː / or / ˈkeɪ /), also spelled caye or key, is a small, low - elevation, sandy island on the surface of a coral reef . Cays occur in tropical environments throughout the Pacific, Atlantic and Indian Oceans (including in the Caribbean and on the Great Barrier Reef and Belize Barrier Reef). </P> <P> A cay forms when ocean currents transport loose sediment across the surface of a reef to a depositional node, where the current slows or converges with another current, releasing its sediment load . Gradually, layers of deposited sediment build up on the reef surface . Such nodes occur in windward or leeward areas of reef where surfaces sometimes occur around an emergent outcrop of old reef or beach rock . </P>

The difference between a key and an island
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