The British Indian Ocean Territory (BIOT) is an archipelago of 55 islands in the Indian Ocean, located south of India. It is situated approximately halfway between Africa and Indonesia. The islands form a semicircular group with an open sea towards the east. The largest, Diego Garcia, is located at the southern extreme end. It measures and accounts for almost three-quarters of the total land area of the territory. Diego Garcia is the only inhabited island and is home to the joint UK-US naval support facility. Other islands within the archipelago include Danger Island, Three Brothers Islands, Nelson Island, and Peros Banhos, as well as the island groups of the Egmont Islands, Eagle Islands, and the Salomon Islands. Physical geography BIOT is an archipelago of 55 islands. They were annexed by the UK in 1965 under the Treaty of Paris from a much larger archipelago which in 1804 consisted of 2,300 independent islands. BIOT is situated in the Indian Ocean near the Equator. It is roughly halfway between Africa and Indonesia, about southwest of India. It is situated approximately from South India and to the south of the Maldives With a coastline stretching , it is the southern extension of the Chagos-Laccadive Ridge. The Chagos Islands archipelago are northeast of Mauritius, while Agalega Islands are due north. The islands are characterised as coral atolls whose formation occurred at the summits of volcanic mountains these being submerged. The terrain is flat and low, with most areas not exceeding above sea level. The climate is tropical marine; hot, humid, and moderated by trade winds. It is located outside the route of the cyclones. Marine reserve The lagoon that surrounds the atoll has an area of about . The maximum water depth in the lagoon is about . The width of the coral reef varies from with a shallow depth of about on the seaward side. The area covered by the fringing seaward reef shelf is about . The bed slope noted at the outer edge of the reef shelf is steep towards the deeper end; the depth drops to more than in some areas within distance from the shore. In 2010, the whole territory, as well as of ocean around the islands, was declared a marine reserve. It is known formally as the Chagos Marine Protected Area, because it is a "pristine ocean ecosystem now representing 16% of the world's fully protected coral