The Araguaia River ( , Karajá: ♂ Berohokỹ [beɾohoˈkə̃], ♀ Bèrakuhukỹ [bɛɾakuhuˈkə̃]) is one of the major rivers of Brazil though it is almost equal in volume at its confluence with the Tocantins. It has a total length of approximately 2,627 km. Geography The Araguaia River comes from Goiás-Mato Grosso south borders. From there it flows northeast to a junction with the Tocantins near the town of São João. Along its course, the river forms the border between the states of Goiás, Mato Grosso, Tocantins and Pará. Roughly in the middle of its course the Araguaia splits into two forks (with the western one retaining the name Araguaia and the eastern one being called the Javaés River). These later reunite, forming the Ilha do Bananal, the world's largest river island. The vein of the Javaés forms a broad inland where it pours back into the main Araguaia, a 100,000 hectare expanse of igapós or flooded forest, blackwater river channels, and oxbow lakes called Cantão, protected by the Cantão State Park. It is one of the biologically richest areas of the eastern Amazon, with over 700 species of birds, nearly 300 species of fish, large populations of species such as the giant otter, the black caiman, the pirarucú, one of the world's largest freshwater fish, and the Araguaian river dolphin (or Araguaian boto), all occurring within a large area. A large portion of the Araguaia's course is navigable all year, but the river below the Cantão wetlands is interrupted by rapids. The middle and lower basin of the river is in the Xingu–Tocantins–Araguaia moist forests ecoregion. The combined watershed of Araguaia and Tocantins rivers (named the Araguaia Tocantins Basin) covers approximately 9.5% of Brazil's national territory. This area is an integral part of the Amazon biome; however, the Araguaia River is not a tributary of the Amazon. "Araguaia" means "River of the macaws" in the native Tupi language. Tributaries Its principal tributary is the Rio das Mortes, which rises in the Serra de São Jerônimo, near Cuiabá, Mato Grosso, and is navigable to Pará. Other important tributaries include the Bonito, Garcas, Tapirape and the Formoso or Cristalino on the west, and the Pitombas, Claro, Vermelho, Tucupa and Chavante on the east. History It was explored in part by Henri Coudreau in 1897. From 1972 to 1974 this region was the scene of a conflict between left-wing guerrilla movements and forces supporting