Great Barrier Reef, largest complex of coral reef in the world, c.1,250 mi (2,000 km) long, in the Coral Sea, forming a natural breakwater for the coast of Queensland, NE Australia. Composed of more than 2,800 individual reefs, the Great Barrier Reef is separated from the mainland by a shallow lagoon from 10 to 100 mi (16-161 km) wide. In some places it is more than 400 ft (122 m) thick. A major tourist attraction, the reef has many islets, coral gardens, and unusual marine life. The Great Barrier Reef Marine Park, more than 130,000 sq mi (340,000 sq km), encompasses most of the reefs and interreefal areas as well as the neighboring lagoon and a large section of the continental shelf. It is the largest UNESCO World Heritage Area.

Extensive complex of coral reefs, shoals, and islets in the Pacific Ocean, off the northeastern coast of Australia. The largest deposit of coral in the world, it extends for more than 1,250 mi (2,000 km) along the coast of Queensland and has an area of some 135,000 sq mi (350,000 sq km). The reef has been formed over millions of years from the skeletons of a mass of living marine organisms. In addition to at least 300 species of hard coral, marine life includes anemones, worms, gastropods, lobsters, crayfish, prawns, crabs, and a variety of fishes. Encrusting red algae form the purplish red algal rim that is one of the reef's characteristic features. A major tourist attraction, nearly all of it is within Great Barrier Reef National Park; the reef was designated a UNESCO World Heritage site in 1981.

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