The Great Barrier Reef is the world's largest coral reef. It is near the coast of Queensland, Australia. It is made up of nearly 2900 coral reefs and over 600 islands. It is 327,800 km² big and 2600 km long. It has been listed an important World Heritage Site by UNESCO. The Great Barrier Reef is the largest structure made by living things. It can be seen from outer space. The Reefs are threatened.