Great Barrier Reef unlike a breakwater or garden wall

Far from being a barrier, the world's most famous reef is an enormous ecosystem comprised of living coral. The aerial view reveals its overall nature best.

Approached by boat, the reef is visible first as islets with waves breaking against them. Seen from below the waterline, the variety of coral of every conceivable shape and size is part of a teeming city of sea life, including enormous schools of fish. Below left, tiny fish swim along a sandy highway between coral cliffs.