User: What is the largest coral reef system in the world?
Assistant: The world's largest coral reef system is The Great Barrier Reef and is located in the Coral Sea, off the coast of Queensland, Australia. The Great Barrier Reef consists of over 900 islands and 2,900 individual reefs stretching for over 2,300 kilometres (1,400 mi) over an area of approximately 344,400 square kilometres (133,000 sq mi). The Great Barrier Reef can be seen from outer space and is the world's biggest single structure made by living organisms. This reef structure is composed of and built by billions of tiny organisms, known as coral polyps. In 1981 The Great Barrier Reef has been selected as a World Heritage Site.