The Great Barrier Reef is the largest group of coral reefs in the world and one of Australia's most popular tourist attractions. The reef is actually a broken chain of more than 2500 reefs, which runs approximately 2010 kilometres along the northeast coast of Australia. Many small islands are also scattered throughout the reef. The waters around the reef remain warm all year. These warm waters and the beauty of the coral formations attract large numbers of swimmers and skin divers to the reef. The coral that forms the Great Barrier Reef is made of hardened skeletons of dead water animals called polyps. Billions of living coral polyps from approximately 400 different species are attached to the reef. Among these species are the staghorn coral, brain coral, honeycomb coral, leaf coral, table coral, and mound coral. The polyps come in a rainbow of colours, including blue-green, purple, red, and yellow. In addition to the coral polyps, the reef supports a fascinating variety of life, including about 1500 species of fish. These include angel fish, cod, manta rays, mackerel, butterfly fish, and surgeonfish crabs, giant clams, shrimps, crayfish, sea urchins, sea stars, sea cucumbers, sea fans, sponges, sea anemones.