The Great Barrier Reef lies off the northeastern coast of Australia and is the largest structure ever made by living organisms including human beings, consisting of the skeletons of tiny coral polyps and hydrocorals bounded together by the soft remains of coralline algae and microorganisms.

The Great Barrier Reef is over 1,250 mi (2,000 km) long and is 80,000 mi² (207,000 km²) in surface area, which is larger than the island of Great Britain. It snakes along the coast of the continent of Australia, roughly paralleling the coast of the State of Queensland, at distances ranging 10–100 mi (16–160 km) from the shore. The reef is so prominent a feature on Earth that it has been photographed from satellites. The reef is located on the continental shelf that forms the perimeter of the Australian landmass where the ocean water is warm and clear. At the edge of the continental shelf...