A barrier reef is a type of coral reef that is separated from the shoreline by a deep lagoon. It is usually found in tropical and subtropical waters, and is made up of living corals and other organisms. The GREAT Barrier Reef is the largest barrier reef in the world, located off the coast of Australia. It is composed of over 2, 900 individual reefs and 900 islands, stretching for over 2, 300 kilometers. It is home to a wide variety of marine life, including fish, turtles, and dolphins.