Barrier Reefs
Barrier reefs are parallel the coastline but are separated by deeper, wider lagoons. At their shallowest point they can reach the water's surface forming a "barrier" to navigation.
The world's largest example of this reef type is the 1200-mile long Great Barrier Reef off the NE coast of Australia. The GBR is not actually a single reef as the name implies, but rather a large complex consisting of many reefs.