The Rowley Shoals, located approximately 170 miles (275 kilometers) off the northwest coast of Western Australia, offer a unique opportunity to dive or snorkel in a pristine coral reef ecosystem. The warm tropical waters in this part of the Indian Ocean have created a favorable habitat for large schools of fish and the formation of vivid colored coral colonies. Game fish, notably sailfish, are also abundant. These pear shaped coral atolls are spaced evenly near the edge of the Australian continental shelf. They include inner lagoons that range from 33 to 66 feet (10 to 20 meters) deep, the surrounding reefs, and sand cays. From southwest to northeast (bottom to top) the names of these three structures are Imperieuse Reef, Clerke Reef, and Mermaid Reef. Imperieuse Reef covers an area of approximately 65 square miles (169 square kilometers).