Chagos Archipelago

The Chagos Archipelago (, also UK: ) or Chagos Islands is a group of coral atolls, reefs and submerged banks in the central Indian Ocean, at the southern end of the Chagos–Laccadive Ridge. It lies 1,188 nautical miles (2,200 km) north-east of the island of Mauritius and, at its closest point, 269 nautical miles (500 km) south of the Maldives. Five atolls carry islands: Diego Garcia, Peros Banhos, the Salomon Islands, the Egmont Islands and the Great Chagos Bank, described as the world's largest atoll by area; the others are reefs and banks, most of them submerged. The 55 to 59 islands are small and low, with a total land area of about 53 km2 (20 sq mi), more than half of it on Diego Garcia, while the archipelago's 200-nautical-mile zone covers some 640,000 km2 (247,000 sq mi). The archipelago has more than 60,000 square kilometres (23,000 sq mi) of shallow reef and limestone platform, and in 2012 Sheppard and colleagues estimated that it held between a quarter and a half of the Indian Ocean's reef area remaining in excellent condition. Largely free of local pollution, fishing and coastal development, its reefs serve as a scientific reference site, although marine heatwaves in 1998 and 2015–2016 killed much of their coral. Eighteen species of seabird breed in the islands, and green and hawksbill turtles nest on their beaches. Diego Garcia was designated a Ramsar site in 2001, and in 2010 the United Kingdom declared the waters around the archipelago, except Diego Garcia, a marine protected area. Portuguese navigators charted the islands in the 16th century. From the 1780s they were settled from Mauritius, then the French colony of Île de France, where planters were granted concessions for coconut plantations worked by enslaved people brought mainly from Madagascar and Mozambique. After the Treaty of Paris the United Kingdom administered the archipelago as a dependency of the colony of Mauritius until 1965, when it detached the islands to form the British Indian Ocean Territory. Between 1967 and 1973 the whole population, the Chagossians, was either prevented from returning or removed, most of them to Mauritius, and a joint British–American military base was built on Diego Garcia. The islands have no permanent inhabitants; around 2,000 people, mostly military personnel and contractors, are ordinarily present on Diego Garcia, and since February 2026 a small group of Chagossians has lived without permits on Île du Coin. Mauritius claims the archipelago, which it says the United Kingdom detached unlawfully before Mauritian independence. In 2019 the International Court of Justice advised that the decolonisation of Mauritius had not been lawfully completed and that the United Kingdom should end its administration of the archipelago "as rapidly as possible", and the United Nations General Assembly demanded its withdrawal in resolution 73/295. On 22 May 2025 the two governments signed a treaty under which the United Kingdom would recognise Mauritian sovereignty over the whole archipelago and keep the base on Diego Garcia for an initial 99 years; as of October 2026 it had not entered into force.

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