Great Barrier Reef
Coral reef system in Queensland, Australia
The largest coral reef system in the world: more than 2,900 separate reefs and 900 islands, stretching over 2,300 kilometres (1,400 mi) and covering about 344,400 square kilometres (133,000 mi²). It lies in the Coral Sea, off the coast of Queensland, Australia.
Photo: NASA, by MISR, Public domain