barrier reef 
noun
A coral reef close and running parallel to the shore but separated from it by a channel of deep water.Reefs are generally divided into three categories; the barrier reef, the atoll, and the fringing reef....
- Closer contact reveals that sport divers who come to these clear, southern waters protected by a barrier reef, fearlessly feed the large group of stingrays which gather in this region.
- It is a 100-hectare tropical garden on the raised coral of the barrier reef surrounding the lagoon.