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[[File:Blue Linckia Starfish.JPG|thumb|right|300px|A typical coral reef and what lives there]]

A '''reef''' is a [[Rock (geology)|rock]], [[sandbar]], or other feature below the water surface (less than 80 meters below low water).

The best-known reefs are the [[coral reefs]] in tropical waters. They are built by [[coral]]s and [[calcareous]] [[algae]]. Artificial reefs such as [[shipwreck]]s are sometimes created to attract fish and other organisms.

[[File:Vanatinai, Louisiade Archipelago.jpg|thumb|left|300px|Reefs in the [[Louisiade Archipelago]]]]

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[[Category:Reefs| ]]