Coral reefs are generally recognized to fall into 3 main types: fringing, barrier and atoll.

Fringing Reef

Fringing coral reefs:  Fringing reefs grow near the coastline and are separated from the shore by a shallow and narrow channel of water. These reefs are usually narrow and recently formed.

The Great Barrier Reef

Barrier coral reefs: Barrier reefs are much broader and will grow farther away from the coastline. They are separated from land by a much deeper and wider stretch of water. A famous example is the Great Barrier Reef in Australia.

Atoll: Lighthouse Reef Belize

Atoll coral reefs: Atolls are large ring-shaped corals that are away from the coast, with a lagoon in the middle. The emergent part of the reef often has accumulated sediments and vegetation.  Atolls are usually formed when volcanic islands surrounded by fringing reefs sink, and the reefs continue to grow to form circles with lagoons in the middle. They can also be formed by rising sea levels.