Chagos Archipelago

History

Early history

According to Southern Maldivian oral tradition, local traders and fishermen were occasionally lost at sea and became stranded in one of the islands of the Chagos. Eventually they were rescued and brought back home. However, these islands were judged to be too far away from the Maldives to be settled permanently by Maldivians. Thus, for many centuries, the Chagos were ignored by their northern neighbours.

16th to 19th century

The first Europeans to become aware of the archipelago were Portuguese explorers. Although the Portuguese navigator Pedro de Mascarenhas (1470 – 23 June 1555) is credited with having encountered the islands during his voyage of 1512–13, there is little corroborative evidence; cartographic analysis points to 1532 or later. Portuguese seafarers named the group Bassas de Chagas, Chagas (lit. 'wounds') referring to the Holy Wounds of the crucifixion of Jesus. They also named some of the atolls, such as Diego Garcia and Peros Banhos Atoll, mentioned as Pedro dos Banhos in 1513 by Afonso de Albuquerque. This lonely and isolated group, economically and politically uninteresting to the Portuguese, was never made part of the Portuguese Empire.

The earliest description of the Chagos was written by Manoel Rangel, a castaway from the Portuguese ship Conceição which ran aground on the Peros Banhos reefs in 1556.

The oldest known written document claiming the Chagos is attributed to King Hassan IX of the Maldives in the year 1561. The French were the first European colonial power to lay claim to the Chagos after they settled Île Bourbon (now Réunion, in 1665) and Isle de France (now Mauritius, in 1715). The French began issuing permits for companies to establish coconut oil plantations on the Chagos in the 1770s.

On 27 April 1786 the Chagos Islands and Diego Garcia were claimed for Great Britain. However, the territory was ceded to Britain by treaty only after Napoleon's defeat, in 1815. The Chagos were governed from Mauritius, which was by that time also a British colony.

In 1793, when the first successful colony was founded on Diego Garcia, the largest island, coconut plantations were established on many of the atolls and isolated islands of the archipelago. The workers were enslaved by the British and not freed until 1840, after which time many of the workers descended from those who had earlier been enslaved. They formed an inter-island culture called Ilois, a French Creole word meaning 'islanders'.

Commander Robert Moresby made a survey of the Chagos on behalf of the British Admiralty in 1837–1838. After Moresby had taken measurements of most of the atolls and reefs, the archipelago was charted with relative precision for the first time.

Moresby's survey

Robert Moresby was a captain of the East India Company's Bombay Marine/Indian Navy who distinguished himself as a hydrographer, maritime surveyor and draughtsman.

After his completion of the Red Sea Survey, Moresby was sent to chart various coral island groups lying across the track of India-to-Cape trade. In 1834–1836 Moresby, assisted by Lieutenants Christopher and Young, undertook the difficult cartography of the Maldive Islands, drawing the first accurate maritime charts of this complicated Indian Ocean atoll group (Admiralty Charts). These charts were printed as three separate large maps by the Hydrographic Service of the Royal Navy.

Moresby's survey of the Atolls of the Maldives was followed by the Chagos Archipelago. where he conducted "a thorough scientific survey". He planted 30 breadfruit trees in Diego Garcia Island, the largest of the group. Moresby reported that "there were cats and chickens on the island".

20th century

On 31 August 1903 the Chagos Archipelago was administratively separated from the Seychelles and attached to Mauritius.

Before granting independence to Mauritius, the United Kingdom paid £3 million in compensation to the Mauritius Government and made several undertakings regarding the future status of the Chagos Archipelago. These included a commitment that the archipelago would be returned to Mauritius if it was no longer needed for defence purposes, assurances that Mauritius would retain access to navigational and meteorological facilities as well as fishing rights, and an agreement that any benefits from minerals or oil discovered in or near the Chagos Archipelago would revert to Mauritius. The compensation was intended to support development projects and address the resettlement of the displaced Chagossian community, though its adequacy and distribution have remained subjects of controversy. Various press articles have wrongly suggested that the £3 million payment was for the purchase of the islands from Mauritius, when in fact it was compensation tied to the detachment of the archipelago and broader commitments made by the British government.

On 25 May 1967, less than two years after the agreement with Premier Seewoosagur Ramgoolam, Prime Minister Harold Wilson attended a Cabinet Committee meeting alongside the Chancellor of the Exchequer and the Secretaries of State for Commonwealth Affairs, Economic Affairs, Defence, and the Home Department. During this meeting, the Commonwealth Secretary noted that at the time of the 1965 agreement, Mauritian ministers were unaware of Britain's negotiations with the United States for a financial contribution toward the compensation. Mauritian officials were also informed that there would be no additional contribution from the United States, as this was a matter solely between the UK and Mauritius. The British government made it clear that the £3 million was the maximum it could afford and that if Mauritius did not accept the proposal, the UK would not proceed with arrangements for granting independence.

During the same meeting, the Secretary of State for Defence stated that when the British Indian Ocean Territory was established, the UK had arranged compensation for both Mauritius and the Seychelles for the detachment of islands, with a total budget of approximately £10 million. The United States had agreed to contribute up to half of this amount, with a maximum of £5 million. To avoid potential embarrassment in the US Congress, the US government requested that its financial contribution remain secret. As a result, it was arranged that the US contribution would be concealed by waiving certain payments owed by the UK to the US in connection with the development of the Polaris missile program.

On 30 December 1966, the United States and the United Kingdom executed an agreement through an Exchange of Notes which permit the United States Armed Forces to use any island of the BIOT for defence purposes for 50 years, until December 2016, followed by a 20-year optional extension (to 2036) to which both parties must agree by December 2014. As of 2010, only the atoll of Diego Garcia has been transformed into a military facility.

In 1967 the British Government bought the entire assets and real property of the Seychellois Chagos Agalega Company, which owned all the islands of the BIOT, for £660,000, equivalent to £13.6 million in 2024, and administered them as a government enterprise while awaiting US funding of its proposed facilities, with an interim objective of paying for the administrative expenses of the new territory. The plantations, under their previous private ownership and under government administration, proved consistently unprofitable due to the introduction of new oils and lubricants in the international marketplace and the establishment of vast coconut plantations in the East Indies and the Philippines.

Between 1967 and 1973, the population was forcibly removed from the islands and moved to Mauritius and the Seychelles to make way for a joint United States–United Kingdom military base on Diego Garcia. In March 1971, United States naval construction battalions (Seabees), arrived on Diego Garcia to begin the construction of the Communications Station and an airfield. To satisfy the terms of an agreement between the United Kingdom and the United States for an uninhabited island, the plantation on Diego Garcia was closed in October of that year.

The plantation workers and their families were initially deported to the plantations on Peros Banhos and Salomon atolls in the group; those who requested were transported to the Seychelles or Mauritius. In 1972, the UK closed the remaining plantations (all being now uneconomic) of the Chagos, and deported the Ilois who would have faced economic hardship to the Seychelles or Mauritius. The independent Mauritian government refused to accept these further displaced islanders without payment and in 1973, the United Kingdom agreed and gave them an additional £650,000, equivalent to £8.7 million in 2024, as reparation payments to resettle the people. Some people were of the view that they were rehoused and employed under worse conditions than other Mauritians. The islands were becoming costly to live in due to industrial moves away from coconut oils and copra fibre markets and the success of larger plantations in the far east.

Since 2000

In 2002, Diego Garcia was used twice for US rendition flights.

On 13 October 2009, the Cabinet of the Maldives Government decided to see if the Maldives can claim for an extended continental shelf.

On 26 July 2010, the Republic of Maldives submitted to the Commission on the Limits of the Continental Shelf, in accordance with Article 76, paragraph 8, of the United Nations Convention on the Law of the Sea, information on the limits of the continental shelf beyond 200 nautical miles (370 km; 230 mi) from the baselines from which the breadth of the territorial sea is measured.

On 1 April 2010, the British government announced the establishment of the Chagos Marine Protected Area as the world's largest marine reserve. At 640,000 km² (250,000 sq mi), it is larger than both France and the US state of California. It doubled the total area of environmental no-take zones worldwide. On 18 March 2015, the Permanent Court of Arbitration unanimously held that the marine protected area (MPA) which the United Kingdom declared around the Chagos Archipelago in April 2010 violates international law. Anerood Jugnauth, Prime Minister of Mauritius, pointed out that it is the first time that the United Kingdom's conduct with regard to the Chagos Archipelago has been considered and condemned by any international court or tribunal.

On 20 December 2010 Mauritius initiated proceedings against the United Kingdom under the United Nations Convention on the Law of the Sea (UNCLOS) to challenge the legality of the Chagos Archipelago MPA.

The issue of compensation and repatriation of the former inhabitants of several of the archipelago's atolls, exiled since 1973, continued in litigation, and in 2010 it was submitted to the European Court of Human Rights by a group of former residents.

Litigation continued in 2012 regarding the right of return for the displaced islanders and Mauritian sovereignty claims. In addition, advocacy on the Chagossians' behalf continues both in the United States and in Europe. In 2018, Mauritius took the matter to the International Court of Justice for an advisory opinion, against British objections.

2014 feasibility study for resettlement

In 2014, a Feasibility Study for the Resettlement of the British Indian Ocean Territory was undertaken for the UK Government by consultants from KPMG.

The objectives of the study were to assess costs and sustainability of resettlement over five, ten, and twenty years, evaluate economic self-sufficiency, risks, and environmental implications and explore potential resettlement options ranging from small-scale pilot projects to larger-scale resettlements. It included consultations with the Chagossian community and environmental assessments.

Large-scale resettlement (1,500 people), medium-scale (500 people), and a pilot scheme (150 people) were proposed. Diego Garcia was a preferred location due to existing infrastructure, with Île du Coin and Boddam also being provisional initial candidate sites.

Chagossians expressed a strong preference for permanent resettlement, not temporary visits. They emphasized the need for modern living standards, environmental conservation, and access to UK-level education and healthcare.

Because most islands are low-lying and vulnerable to climate change, the study concluded environmental protections and monitoring would be critical in the case of resettlement.

Tourism, fishing, and environmental monitoring and research were outlined as potential employment opportunities, while subsistence living was also considered. High-end and eco-tourism were especially noted as potential revenue generators.

Amendments to BIOT's legal framework would be required to facilitate resettlement. It was suggested that governance models could draw from other small British Overseas Territories like Pitcairn and Ascension Island.

In November 2016, the United Kingdom restated it would not permit Chagossians to return to the islands.

.io domain name dispute

In July 2021, the Chagos Refugees Group UK submitted a complaint to the Irish government against domain-name speculators Paul Kane and Ethos Capital subsidiary Afilias, seeking repatriation of the .io (that is, Indian Ocean) country-code top-level domain and payment of back royalties from the US$7 million per year in revenue generated from it. This attempt cites consumer and human rights violations of the OECD's 2011 Guidelines for Multinational Enterprises rather than multistakeholder representation under ICANN policy. The domain has enjoyed commercial success, particularly among cryptocurrency companies. In September 2023, all three complaints submitted regarding the top-level domain were concluded without agreement.

As a consequence of the UK ceding the territory, the .io domain faces potential retirement under ICANN policy if the territory's ISO 3166-1 country code is removed, which would trigger a minimum five-year phase-out period.

2026 resettlement mission

On 16 February 2026, four British Chagossians landed on Île du Coin, Chagos Islands, to establish a permanent settlement, without seeking government permission. They became the first Chagossians to live on the islands since the expulsion of the Chagossians in 1971. An injunction by the Chief Justice of the British Indian Ocean Territory three days later prevented the immediate deportation of the islanders.

Sovereignty dispute

The Chagos had been administered from imperial offices in Mauritius since the 18th century when the French first named the islands. All of the islands forming part of the French colonial territory of Isle de France (as Mauritius was often then known) were ceded to the British in 1810 under the Act of Capitulation. In 1965, in planning before Mauritian independence, the UK split the archipelago from the territory of Mauritius to form the British Indian Ocean Territory, looking to provide the United States, which was the country's main creditor following the turmoil of the Second World War, with an uninhabited island base.

The United Nations' resolutions on self-determination deprecated the parcelling up of imperial territories before independence, without its endorsement and local support, mindful of the Partition of India which provided the strong governments sought by the separate factions but failed to ensure a relatively peaceful transfer of power in many places. Mauritius has repeatedly stated that the British claim that the Chagos Archipelago is one of its territories thwarted its claim to what would be widely considered part of the Mauritian colony and also breached UN resolutions. The UK has stated that the Chagos will be assigned to Mauritius once the islands are no longer required for defence purposes.

The island nation of Mauritius claims the Chagos Archipelago (which is coterminous with the BIOT), including Diego Garcia. Maldives states that the UK's claim to a 200-nautical-mile (370 km; 230 mi) Exclusive Economic Zone around the Chagos Archipelago is invalid as the islands are considered uninhabited. A subsidiary issue is the Mauritian opposition to the 1 April 2010 UK Government's declaration that the BIOT is a Marine Protected Area with fishing and extractive industry (including oil and gas exploration) prohibited.

On 16 November 2016, the UK Foreign Office maintained their ban on repatriation of the islands. In response to this decision, the Prime Minister of Mauritius expressed his country's plan to advance the sovereignty dispute to the International Court of Justice. British Foreign Secretary Boris Johnson sought Indian assistance for resolving the dispute involving the UK, the US, and Mauritius. India has maintained considerable influence in Mauritius through deep cultural and economic ties. India has maintained that the matter of whether or not to proceed with the UN General Assembly move is a decision for the Mauritian government to make.

On 23 June 2017, the United Nations General Assembly (UNGA) voted in favour of referring the territorial dispute between Mauritius and the United Kingdom to the International Court of Justice (ICJ). The motion was approved by a majority vote with 94 voting for and 15 against. On 25 February 2019, the International Court of Justice advised that in its opinion:

• "at the time of its detachment from Mauritius" the "Chagos Archipelago was clearly an integral part of that non-self-governing territory";
• the United Kingdom's purported detachment of the Chagos Archipelago "was not based on the free and genuine expression of the will of the people concerned";
• at the time of the purported detachment, "obligations arising under international law and reflected in the resolutions adopted by the General Assembly during the process of decolonization of Mauritius require[d] the United Kingdom, as the administering Power, to respect the territorial integrity of that country, including the Chagos Archipelago";
• the "detachment" was therefore "unlawful" such that "the process of decolonization of Mauritius was not lawfully completed when Mauritius acceded to independence in 1968"
• "the United Kingdom's continued administration of the Chagos Archipelago constitutes a wrongful act entailing the international responsibility of that State";
• this "unlawful act" is "of a continuing character" and "the United Kingdom is under an obligation to bring to an end its administration of the Chagos Archipelago as rapidly as possible"; and
• "all Member States [of the United Nations] are under an obligation to co-operate with the United Nations in order to complete the decolonization of Mauritius."

The British government rejected any jurisdiction of the court to deliberate these matters.

On 22 May 2019, the United Nations General Assembly debated and adopted a resolution that affirmed that the Chagos archipelago "forms an integral part of the territory of Mauritius." The resolution demanded that the UK "withdraw its colonial administration ... unconditionally within a period of no more than six months." 116 states voted in favour of the resolution, 56 abstained and 5 countries supported the United Kingdom. During the debate, the Mauritian Prime Minister, Sir Anerood Jugnauth, described the expulsion of Chagossians as "akin to a crime against humanity", while the United Kingdom continued to assert that it had no doubt about its sovereignty over the archipelago. The Maldives were one of the countries which supported the UK in the General Assembly vote. It stated that, if the Chagos Archipelago became inhabited, the Maldives' claim to an extension of its Exclusive Economic Zone would be affected. China abstained in the 2019 UN vote, which was a step towards reaching an agreement to return the Chagos Archipelago to Mauritius. The resolution's immediate consequence was that the UN and other international organisations became bound by UN law to support the decolonisation of the Chagos Islands.

On 28 January 2021, the United Nations' International Tribunal for the Law of the Sea (ITLOS) confirmed the International Court of Justice ruling and ordered Britain to hand over the Chagos Archipelago to Mauritius. The ITLOS Special Chamber affirmed that: "it is inconceivable that the United Kingdom, whose administration over the Chagos Archipelago constitutes a wrongful act of a continuing character and thus must be brought to an end as rapidly as possible, and yet who has failed to do so, can have any legal interests in permanently disposing of maritime zones around the Chagos Archipelago by delimitation".

In August 2021, the Universal Postal Union banned BIOT stamps from being used in the BIOT, a move Mauritian Prime Minister Pravind Jugnauth called a "big step in favour of the recognition of the sovereignty of Mauritius over the Chagos".

On November 26, 2021, Mauritius amended its Criminal Code through the Criminal Code (Amendment) Act 2021 to introduce Section 76B, which criminalizes actions that misrepresent Mauritius' sovereignty over any part of its territory. The law applies to individuals acting under the authority, instructions, or financial support (direct or indirect) of a foreign state and imposes penalties of a fine or imprisonment of up to 10 years. Offenses include producing, distributing, or marketing coins, stamps, maps, or official documents that misrepresent Mauritius' sovereignty, as well as instructing others to do so. A "foreign state" under this provision refers to any country that an international court or tribunal has determined to have no valid claim over any part of Mauritius' territory.

On 14 February 2022, a delegation from Mauritius, including the Mauritian ambassador to the UN, raised the Mauritian flag on the Chagossian atoll of Peros Banhos. The move was done in the context of a scientific survey of Blenheim Reef but was regarded as a formal challenge to British sovereignty over Chagos.

On 3 November 2022, the British Foreign Secretary James Cleverly announced that the UK and Mauritius had decided to begin negotiations on sovereignty over the British Indian Ocean Territory, taking into account the recent international legal proceedings. Both states had agreed to ensure the continued operation of the joint UK/US military base on Diego Garcia.

Although these talks included the resettlement of expelled Chagossians, Cleverly's successor as British foreign secretary, David Cameron, later ruled out a return of the islanders.

On 3 October 2024, the UK Government made a joint statement with the Mauritian government that they had negotiated for the sovereignty of the Chagos Islands following two years of negotiation whilst still enabling the running of the American military base on Diego Garcia, thereby ruling out the right of return of the Chagossians to that specific island. The Chagossian people living in the UK have criticised the deal for not having included the Chagossian community in the decision-making process. and expressed concerns that their interests may not be fully safeguarded under Mauritian administration. However, many Chagossians, including those in Mauritius, support Mauritian sovereignty. The Chagos Refugees Group, the largest Chagossian advocacy organization, has been a leading voice for this position. Its leader, Olivier Bancoult, described the UK's decision to return the Chagos Archipelago to Mauritius and allow Chagossians to resettle on the outer islands as a significant step and an acknowledgment of past injustices. On the same day, former Maldivian President Mohamed Nasheed stated that the decision to hand over the Chagos Islands to Mauritius, despite the Maldives' claims, was unacceptable. On 6 October 2024, the Democrats Party of the Maldives expressed concern that Maldives President Mohamed Muizzu's administration had not been making efforts to assert the Maldives' claim over the Chagos Archipelago, as promised in the presidential pledge. In December 2024, Muizzu sent an official letter to the United Kingdom, which he said asserted the Maldives' strong historical claim to the archipelago, although the specific text of the letter was not released.

The deal was put on hold following the 2024 United States presidential election to allow consideration from the new incoming US administration. On 27 February 2025, speaking in the Oval Office alongside UK Prime Minister Sir Keir Starmer, US President Donald Trump stated that he was willing to support the agreement to transfer sovereignty of the Chagos Islands to Mauritius. In April, Trump signed off on the deal.

There has been a consistent theme of negotiations and decisions about the Chagos Islands being made without directly involving or consulting the Chagossian community. This exclusion from the sovereignty negotiations between the UK and Mauritius has fuelled opposition among Chagossians, who feel their voices have been deliberately ignored in determining the future of their homeland. They demand full inclusion in any discussions or treaties regarding the Chagos Islands.

The Chagossians have been engaged in numerous legal battles over their right to return and the sovereignty of the islands. Legal actions like those initiated by Bernadette Dugasse against the UK government for failing to include Chagossians in sovereignty talks further underscore their opposition to decisions made without their input. This reflects a broader struggle for recognition of their rights and sovereignty over their land.

On 22 May 2025 the Prime Minister of the United Kingdom Keir Starmer signed a formal agreement on the transfer of sovereignty of the Chagos Islands to Mauritius. The British Conservative Party subsequently tabled a motion of censure against the agreement signed on 22 May 2025 between Great Britain and Mauritius.

Under the terms of the deal, the strategic atoll of Diego Garcia and its surrounding 39-kilometre (24 mi) buffer zone are immediately leased back to the UK. This arrangement permits the continued operation of the joint UK/US base on the island for the next 99 years, with an additional 40-year extension and a subsequent right of first refusal.

Mauritius will receive an annual rent of £165 million from the UK for the first three years, followed by £120 million annually for the subsequent ten years. Thereafter, the £120 million annual payment will be adjusted for inflation.

In June 2025, the Great British PAC launched a legal action aimed at demonstrating the illegal actions of the British government in signing this restitution agreement.

Chagossian activists submitted a legal submission to the United Nations Human Rights Committee in June 2025, challenging the legitimacy of the UK-Mauritius deal, arguing that it was negotiated without their consent and perpetuates historical injustices.

On June 10, 2025, UN experts called for the suspension of a recently signed agreement between the United Kingdom and Mauritius, warning that it failed to protect the rights of the displaced Chagossian people. "By maintaining a foreign military presence of the United Kingdom and the United States on Diego Garcia and preventing the Chagossian people from returning... the agreement appears to be in contradiction with the Chagossian right of return," according to the experts. The experts criticized the lack of provisions allowing access to cultural sites or the preservation of the Chagossian heritage. They called on the two countries to renegotiate the restitution agreement, stating, "We call for the suspension of ratification of the agreement and the negotiation of a new agreement that fully guarantees the rights of the Chagossian people".

Following the Chagos Archipelago handover agreement, the British government is also due to introduce legislation to implement the agreement, including amending the British Nationality Act 1981 to reflect that the British Indian Ocean Territory is no longer an overseas territory following Parliament's ratification of the treaty, and to empower the British government to make secondary legislation to allow for the continued operation of the Diego Garcia military base.

On May 23, 2025, India welcomed the agreement between the United Kingdom and Mauritius for the transfer of sovereignty over the Chagos Islands, describing it as an important step in completing the decolonization of the island nation "in the spirit of international law and a rules-based order".

On June 25, 2025, the peers of the House of Lords concluded that the government "cannot ignore" the risk of an "adverse decision" jeopardizing Great Britain's right to operate a joint American and British base.

The agreement may be renewed for an additional 40 years after the initial 99-year period, and for an additional period thereafter.

In July 2025, a legal action demanding that the British government consult with the Chagossians before transferring sovereignty of their territory progressed before the High Court. The judicial review, initiated by Chagossian claimant Louis Misley Mandarin with the support of the Great British PAC, was accepted and fast-tracked by the High Court, with a decision set for July 2025.

On 5 January 2026, Conservative peers in the House of Lords forced an amendment that would require a self-determination referendum from Chagossian people before the deal could go ahead, and another that would see Britain stop making payments if "use of the base for military purposes became impossible."

On 20 January 2026, despite having previously agreed to the handover, US President Donald Trump criticized the UK's controversial deal to transfer sovereignty of the Chagos Islands to Mauritius because it includes the Naval Support Facility Diego Garcia, following a meeting between Leader of the Opposition Kemi Badenoch and Speaker of the House Mike Johnson. Trump called it an "act of great stupidity" and "total weakness" that harms national security and benefits rivals like China and Russia. Trump said the move, even with the U.K. retaining a long-term lease on Diego Garcia, undermines Western strength and used it to justify his push to acquire Greenland. The U.K. defended the agreement as ensuring the base's future. On February 18, Trump addressed again UK's deal with Mauritius, criticizing it and writing in Truth: "Do not give away Diego Garcia,". This came as he spoke also about the base could be used to assist American airstrikes on Iran.

In February 2026, UK Secretary of State for Defence, John Healey, was accused by the Conservatives of misleading parliament, by claiming in May 2025, that if the UK did not cede the British Indian Ocean Territory to Mauritius, it could face losing legal rulings "within weeks", and "within just a few years" the base at Diego Garcia "would become inoperable". Healy claimed that "the most proximate, and the most potentially serious" threat was the International Tribunal for the Law of the Sea (ITLOS), however under Article 298 of the United Nations Convention on the Law of the Sea (UNCLOS) there is an exemption for "disputes concerning military activities, including military activities by government".

In March 2026, Justice James Lewis of the British Indian Ocean Territory (BIOT) Court delivered a landmark ruling, affirming that Chagossians have a right of abode on their ancestral islands.

In April 2026, reports say that the deal was paused by the UK, following criticism of the deal by US President Donald Trump. The current parliamentary session also will not allow for enough time for the treaty to be enshrined as UK law.

Development

Actively used structures on the islands are located in the joint defence and Naval Support Facility Diego Garcia. The Plantation House and other structures left behind by the Ilois are still standing, but left abandoned and decaying.

Other uninhabited islands, especially in the Salomon Atoll, are common stopping points for long-distance yachtsmen travelling from Southeast Asia to the Red Sea or the coast of Africa, although a permit is required to visit the outer islands.

People and language

Chagossians

The islanders were known as the Ilois (a French Creole word for 'islanders') and they numbered about 1,000 prior to their forced expulsion. They were of mixed African, South Indian, Portuguese, English, French and Malay descent and worked in the coconut and sugar plantations, or in the fishing and small textile industries. Few remains of their culture have been left, although their language is still spoken by some of their descendants in Mauritius.

The inhabitants of Chagos spoke Chagossian Creole, also known as Ilois creole, a French Creole which has not been extensively researched linguistically. The island names are a mixture of Dutch, French, English and Ilois Creole.

The Ilois who inhabited the islands were forcibly removed by the US and British governments during the late 1960s and early 1970s, the majority of which were abandoned in Mauritius – effectively turning the islands into a military base. While a number of islanders have petitioned for the return of their former homes and their right to return has been recognised by the UN General Assembly, the International Court of Justice, the International Tribunal for the Law of the Sea and the British Indian Ocean Territory Court, the US and UK governments have refused to adhere to these decisions, leaving the Chagossians in exile.

Military personnel and contractors

Around 1,700 armed services personnel of the United States Army, Navy and Air Force and British Royal Navy are stationed on Diego Garcia. They are supported by around 1,500 civilian contractors.

The Catholics are pastorally served by the Roman Catholic Diocese of Port-Louis, which includes the BIOT.

Government

The Government of the BIOT consists of a Commissioner appointed by the King on the advice of the Foreign and Commonwealth Office.

The Commissioner is assisted by an Administrator and small staff, and is based and resident in the Foreign and Commonwealth Office. This administration is represented in the Territory by the Officer commanding British Forces on Diego Garcia, known as the Brit Rep. Laws and regulations are promulgated by the Commissioner and enforced in the BIOT by the British Representative.

Ecology

The Chagos, together with the Maldives and Lakshadweep, forms the Maldives–Lakshadweep–Chagos Archipelago tropical moist forests terrestrial ecoregion. The islands and their surrounding waters are a vast oceanic Environment Preservation and Protection Zone (EPPZ) (Fisheries Conservation and Management Zone (FCMZ) of 544,000 square kilometres (210,000 sq mi)), an area twice the size of the UK's land surface.

The deep oceanic waters around the Chagos Islands, out to the 200 nautical mile limit, include an exceptional diversity of undersea geological features (such as 6000 m deep trenches, oceanic ridges, and sea mounts). These areas almost certainly harbour many undiscovered and specially adapted species. Although the deepwater habitats surrounding the islands have not been explored or mapped in any detail, work elsewhere in the world has shown that high physical diversity of the sea floor is closely linked to a high diversity of species.

The biodiversity of the Chagos archipelago and its surrounding waters is one of the main reasons it is so special. As of 2010, 76 species that call Chagos home were listed on the IUCN Red List of Threatened Species.

Coral

The reefs host at least 371 species of coral including the endemic brain coral Ctenella chagius. Historically, the coral cover was dense and healthy even in deep water on the steep outer reef slopes. Thick stands of branching staghorn coral (Acropora sp) previously protected the low-lying islands from wave erosion. Despite the loss of much of the coral in a bleaching event in 1998 the recovery in the Chagos was remarkable and overall coral cover increased year on year to 2014. High water temperatures, however, caused coral bleaching in both 2015 and 2016 which resulted in the death of more than two-thirds of corals.

Fish

The reefs are also home to at least 784 species of fish that stay near to the shores of the islands including the endemic clownfish (Amphiprion chagosensis) and many of the larger wrasse and grouper that have already been lost from over-fishing in other reefs in the region.

As well as the healthy communities of reef fish there are significant populations of pelagic fish such as manta rays (Manta birostris), whale sharks, other sharks, and tuna. Shark numbers have dramatically declined as a result of illegal fishing boats that seek to remove their fins and also as accidental by-catch in the two tuna fisheries that used to operate seasonally in the Chagos.

Birds

Seventeen species of breeding seabird can be found nesting in huge colonies on many of the islands in the archipelago, and 10 of the islands have been designated Important Bird Areas by BirdLife International. This means that Chagos has the most diverse breeding seabird community in this tropical region. Of particular interest are the large colonies of sooty terns (Sterna fuscata), brown and lesser noddies (Anous stolidus and Anous tenuirostris), wedge-tailed shearwaters (Puffinus pacificus) and red-footed boobies (Sula sula). Land bird fauna is poor and consists of introduced species and recent natural colonisers. Red fody has been introduced and is now widespread.

Mammals

Environments in the Chagos Archipelago provide rich biodiversity and support varieties of cetacean species, such as three populations of blue whales and toothed whales (sperm, pilot, orca, pseudo-orca, risso's and other dolphins such as spinners). Dugongs are now locally extinct but once thrived in the archipelago and Sea Cow Island was named after the presence of the species. Donkeys left behind when the Ilois were relocated also roam free.

Turtles

The remote islands make perfect undisturbed sites for nests of green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) turtles. The populations of both species in Chagos are of global significance given the critically endangered status of hawksbills and the endangered status of green turtles on the IUCN Red List. Chagos turtles had been heavily exploited for two centuries but they and their habitats are now well protected by the government of the British Indian Ocean Territory and are recovering well.

Crustaceans

The coconut crab (Birgus latro) is the world's largest terrestrial arthropod, reaching more than a metre in leg span and 3.5–4 kilos in weight. As a juvenile it behaves like a hermit crab and uses empty coconut shells as protection, but as an adult this giant crab climbs trees and can crack through a coconut with its massive claws. Despite its wide global distribution, it is rare in most of the areas in which it is found. The coconut crabs on Chagos constitute one of the most undisturbed populations in the world. An important part of their biology is the long distances their young can travel as larvae. This means the Chagos coconut crabs are a vital source for replenishing other over-exploited populations in the Indian Ocean region.

Insects

113 species of insect have been recorded from the Chagos Islands.

Plants

The Chagos Islands were colonised by plants once there was sufficient soil to support them—probably less than 4,000 years. Seeds and spores arrived on the emerging islands by wind and sea and from passing seabirds. The native flora of the Chagos Islands is thought to consist of forty-one species of flowering plant and four ferns, as well as a wide variety of mosses, liverworts, fungi and cyanobacteria.

Today the status of the Chagos Islands' native flora depends very much on past exploitation of particular islands. About 280 species of flowering plant and fern have now been recorded on the islands, but this increase reflects the introduction of non-native plants by humans, either accidentally or deliberately. As some of these non-native species have become invasive and pose a threat to the native ecosystems, plans are being developed to control them. On some islands native forests were felled to plant coconut palms for the production of copra oil. Other islands remain unspoiled and support a wide range of habitats, including unique Pisonia forests and large clumps of the gigantic fish poison tree (Barringtonia asiatica). Unspoiled islands provide us with the biological information that we need to re-establish the native plant communities on heavily altered islands. These efforts will ultimately help to improve the biodiversity of the Chagos Islands.

Conservation efforts

Past

Successive UK governments, both Labour and Conservative, have supported environmental conservation of the Chagos. They have committed to treating the whole area as a World Heritage Site. In 2003 the UK government established an Environment (Protection and Preservation) Zone under Article 75 of the UN Convention on the Law of the Sea extending 200 nautical miles from the islands. On eastern Diego Garcia, the largest island of the Chagos and the site of a UK–US military facility, Britain has designated the very large lagoon and the eastern arm of the atoll and seaward reefs as a "wetland of international importance" under the Convention on Wetlands of International Importance (the Ramsar Convention).

Present

On 1 April 2010 Britain announced the creation of the Chagos Marine Protected Area, the world's largest continuous marine protected reserve, with an area of 545,000 km² (210,000 sq mi).

This followed an effort led by the Chagos Environment Network, a collaboration of nine leading conservation and scientific organisations seeking to protect the rich biodiversity of the Chagos Archipelago and its surrounding waters. The Chagos Environment Network cites several reasons for supporting a protected area.

The UK government opened a three-month public consultation, which ended after 5 March 2010, on conservation management of the Chagos Islands and its surrounding waters.

On 1 April 2010 the British government Cabinet established the Chagos Archipelago as the world's largest marine reserve. At 640,000 km² (250,000 sq mi), it is larger than both France and the US state of California. It doubled the total area of environmental no-take zones worldwide. The protection of the marine reserve will be guaranteed for the next five years thanks to the financial support of the Bertarelli Foundation. The setting up of the marine reserve would appear to be an attempt to prevent any repatriation by the inhabitants evicted in the 1960s and 1970s. Leaked US cables have shown the FCO suggesting to its US counterparts that setting up a protected no-take zone would make it "difficult, if not impossible" for the islanders to return. The reserve was then created in 2010.

Permanent Court of Arbitration ruling

On 18 March 2015 the Permanent Court of Arbitration unanimously held that the marine protected area (MPA) that the UK had declared around the Chagos Archipelago in April 2010 violated international law. Anerood Jugnauth, Prime Minister of Mauritius, pointed out that it was the first time that the UK's conduct with regard to the Chagos Archipelago had been considered and condemned by any international court or tribunal. He qualified the ruling as an important milestone in the relentless struggle, at the political, diplomatic and other levels, of successive governments over the years for the effective exercise by Mauritius of its sovereignty over the Chagos Archipelago. The tribunal considered in detail the undertakings given by the United Kingdom to the Mauritian ministers at the Lancaster House talks in September 1965. The UK had argued that those undertakings were not binding and had no status in international law. The tribunal firmly rejected that argument, holding that the undertakings became a binding international agreement upon the independence of Mauritius and had bound the UK ever since. It found that the UK's commitments towards Mauritius in relation to fishing rights and oil and mineral rights in the Chagos Archipelago were legally binding.

The Tribunal also found that the United Kingdom's undertaking to return the Chagos Archipelago to Mauritius when no longer needed for defence purposes was legally binding. This establishes that, in international law, Mauritius has real, firm and binding rights over the Chagos Archipelago and that the United Kingdom must respect those rights. The tribunal went on to hold that the United Kingdom had not respected Mauritius' binding legal rights over the Chagos Archipelago. It considered the events from February 2009 to April 2010, during which time the MPA proposal came into being and was then imposed on Mauritius.

UN expert

On June 10, 2025, UN experts called for the suspension of a recently signed agreement between the United Kingdom and Mauritius, warning that it failed to protect the rights of the displaced Chagossian people. "By maintaining a foreign military presence of the United Kingdom and the United States on Diego Garcia and preventing the Chagossian people from returning... the agreement appears to be in contradiction with the Chagossian right of return," according to the experts. The experts criticized the lack of provisions allowing access to cultural sites or the preservation of the Chagossian heritage. They called on the two countries to renegotiate the restitution agreement, stating, "We call for the suspension of ratification of the agreement and the negotiation of a new agreement that fully guarantees the rights of the Chagossian people".

WikiLeaks cablegate disclosure

According to United States diplomatic cables published by WikiLeaks, the UK and US wanted to safeguard the strategic value of the Chagos Islands.

WikiLeaks published a cable from the US embassy in London to Washington stating:

HMG would like to establish a marine park or reserve providing comprehensive environmental protection to the reefs and waters of the British Indian Ocean Territory (BIOT), a senior Foreign and Commonwealth Office (FCO) official informed Polcouns on May 12. The official insisted that the establishment of a marine park—the world's largest—would in no way impinge on USG use of the BIOT, including Diego Garcia, for military purposes. He agreed that the UK and US should carefully negotiate the details of the marine reserve to assure that US interests were safeguarded and the strategic value of BIOT was upheld. He said that the BIOT's former inhabitants would find it difficult, if not impossible, to pursue their claim for resettlement on the islands if the entire Chagos Archipelago were a marine reserve.

Novels

• Shenaz Patel, Le silence des Chagos, Éditions de l'Olivier, 2005, ISBN 9782879294544
• Caroline Laurent, Rivage de la colère, Les Escales, 2020, ISBN 9782266311915