Corals grow best on the edge outside of the reef facing the open ocean. This edge is called the reef front . Barrier reefs grow further away from the beach shoreline. In the ocean water between the barrier reef and the shoreline lies a protected, calm and often shallow, pond-like body of water called a lagoon. Barrier reefs also have a reef flat covered with ocean water during high tide, but has little or no water on it during low tide.
Many corals grow on the outer reef front but they also grow well in the lagoon.
The part of the reef that faces the lagoon is called the inner reef. The barrier reef acts as a wall that protects the lagoon and the inner reef. Boats often dock in the lagoon for protection against strong waves, but must be careful not to run into the reef where corals are growing in shallow water. Atolls grow in the shape of a circle. In the middle of a circle is a lagoon.