Part 15 of 20
The Chagos Archipelago: the Indian Ocean’s wilderness reefs
In the middle of the Indian Ocean, the Chagos Archipelago holds some of the cleanest, least-disturbed reefs on Earth, inside one of the world’s largest marine reserves.
The Chagos Archipelago is a group of seven atolls and more than 60 islands in the middle of the Indian Ocean. Among them is the Great Chagos Bank, the largest atoll structure in the world. With almost no human population apart from the military base on Diego Garcia, its reefs are among the least disturbed anywhere and a vital reference point for scientists.
Why it’s special
Without fishing, pollution or coastal development, Chagos is what many reefs looked like before people changed them. Its waters are among the cleanest measured, and its reefs hold large populations of sharks, turtles and reef fish, plus seabird colonies on islands cleared of rats. In 2010 the British government declared a marine protected area covering the whole archipelago, one of the largest in the world.
The reef today
Remote doesn’t mean safe from warming seas. During the global bleaching event, about 85% of Chagos reefs were affected and roughly a quarter of the coral died by the end of 2024. Because there are no other local pressures, scientists are watching closely to see how quickly the reefs recover; after earlier bleaching in 1998 and 2016 they recovered strongly.
Who owns Chagos?
The islands were separated from Mauritius by Britain in 1965 to form the British Indian Ocean Territory, and the islanders, the Chagossians, were forcibly removed to make way for the US base on Diego Garcia. In 2025 the UK and Mauritius signed a treaty to transfer sovereignty to Mauritius while keeping the base under a long lease. As of 2026 the treaty had not yet been fully ratified by the UK Parliament, so check the latest position.
Can you visit?
In practice, almost no one can. There are no hotels, no commercial flights and no dive operators, and access has long been restricted to permitted yachts and scientific expeditions. If you want reefs with a similar feel, the Maldives, a few hundred kilometres to the north, is the nearest place to see Indian Ocean atolls; see our guide to the reefs of the Maldives.
What scientists have found
Because Chagos has so few local pressures, it has become one of the world’s most important natural laboratories for reef science. Long-term studies there have shown how quickly reefs can recover when overfishing and pollution are absent, and how heat stress alone can still devastate them. Researchers have also found that the seabird colonies on rat-free islands fertilise nearby reefs, boosting fish growth, which has encouraged rat eradication projects elsewhere in the Indian Ocean.
Seeing reefs like Chagos
Since visiting Chagos isn’t realistic for most people, the best way to see similar reefs is to head for remote, well-protected atolls elsewhere: the outer atolls of the Maldives, Aldabra in the Seychelles (reached only by expedition cruise), or the protected reefs of Palau and Tubbataha on our list. Wherever you go, choose operators that support local conservation.
Book a trip
Compare snorkel trips, dive days and tours for this area on our partner GetYourGuide, with reviews from other travellers and free cancellation on many trips. For the full list, see the world’s top 20 coral reefs, or read about coral bleaching and the future of reefs.
Questions people ask
Can tourists visit the Chagos Islands?
Not in the usual way. There is no tourism infrastructure, and access is restricted.
Why are the Chagos reefs important?
They are among the least disturbed reefs on Earth, which helps scientists understand how reefs cope with heat when there are no other pressures.
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