The largest reef system in the world is the Great Barrier Reef, located off the coast of Queensland, Australia. Spanning over 2,300 kilometers, it comprises over 2,900 individual reefs and 900 islands, making it the most extensive coral reef ecosystem globally. This UNESCO World Heritage Site is renowned for its biodiversity, housing thousands of marine species, including various types of fish, corals, mollusks, and marine mammals. The Great Barrier Reef also plays a significant role in tourism, research, and conservation efforts. However, it faces threats from climate change, pollution, and overfishing, emphasizing the need for environmental protection.