As part of the British Indian Ocean Territory, the Chagos Islands and its surrounding waters comprise about 55 islands and spread over 544,000 square kilometres. Due to their remoteness, the islands have some of the cleanest seas in the world and contain as much as half of the Indian Ocean's remaining healthy reefs, making it one of the most ecologically-sound reef systems on the planet.
The waters around the Chagos Islands, within its 200 mile oceanic exclusive economic zone (EEZ), contain the world's largest coral atoll, at least 1,000 species of fish and endemic corals and reef fish found nowhere else in the world. At least 60 species listed in the International Union for Conservation of Nature's Red List of Endangered Species live in these waters. The islands provide a safe haven for dwindling populations of turtles and hundreds of thousands of breeding sea birds, as well as an exceptional diversity of deepwater habitats, such as trenches reaching approximately 6,000 metres in depth. While these habitats have not been explored or mapped in detail, scientific research has shown a close linkage between great physical sea floor diversity and high species diversity.