There have been reefs off the northeast coast of Australia for around 17 million years, ever since the drifting continent entered tropical waters. Live coral grows on the accumulated skeletons of dead coral, so the Reef as a whole is growing between one and two centimetres annually. Only live coral has colour, with dead coral appearing white.

The colour in coral comes from associated species of algae that serve as food to the coral polyps. Each polyp lives inside a shell of aragonite, a type of calcium carbonate, and the polyps join together to form the distinctive, intricate patterns of coral. The Reef was formed by colonies of coral polyps, which thrive in the warm, shallow waters of the Coral Sea. The section of Reef seen here is towards its northern extremity, known as the Far Northern Management Area. Home to sharks, turtles, and 1500 tropical fish species, the Great Barrier Reef is a popular destination for scuba divers and many cities across the Queensland coast offer daily boat trips for tourists.

Around a third of the Reef is protected as part of Australia's Great Barrier Reef Marine Park, the largest marine park in the world. An area of biodiversity equal in importance to tropical rainforests, the Reef was made a UNESCO World Heritage Site in 1981. Properly speaking, the Great Barrier Reef is an interlinked system of about 3000 reefs and 900 coral islands, divided by narrow passages.

Great barrier reef