The Roosevelt River (Rio Roosevelt, sometimes Rio Teodoro) is a Brazilian river, a tributary of the Aripuanã River about in length. Course The Roosevelt River begins in the state of Rondônia and flows north through tropical rainforest. It is fed by the Capitão Cardoso River, which meets it at the state boundary. In Mato Grosso the river forms the western boundary of the Guariba-Roosevelt Extractive Reserve, a sustainable use unit created in 1996. After entering Amazonas the river forms the border between the Manicoré State Forest, a sustainable use conservation unit created in 2005 and the Guariba State Park, also created in 2005. The river then runs through the Campos Amazônicos National Park, a protected area created in 2006 that holds an unusual enclave of cerrado vegetation in the Amazon rainforest. It continues north until it joins the Aripuanã River. The Aripuanã then flows into the Madeira River, thence into the Amazon. History and exploration Formerly called Rio da Dúvida (“River of Doubt”), the river is named after Theodore Roosevelt, who traveled into the central region of Brazil during the Roosevelt–Rondon Scientific Expedition of 1913–14. The expedition, led by Roosevelt and Cândido Rondon, Brazil's most famous explorer and the river's discoverer, sought to determine where and by which course the river flowed into the Amazon. Roosevelt and his son Kermit undertook the adventure after the former U.S. president's failed attempt to regain the office as the "Bull Moose" candidate in 1912. The Roosevelt-Rondon expedition was the first non Amazonian-native party to travel and record what Rondon had named the "Rio da Dúvida", then one of the most unexplored and intimidating tributaries of the Amazon. Sections of the river have impassable rapids and waterfalls, which hindered the expedition. Roosevelt later wrote Through the Brazilian Wilderness recounting the adventure. After Roosevelt returned doubts were raised on his account of the expedition. Roosevelt promptly rebutted them in a public forum in Washington, D.C., sponsored by the National Geographic Society. In 1927 British explorer George Miller Dyott led a second trip down the river, independently confirming Roosevelt's discoveries. In 1992 a third (modern) expedition was organized, funded, and led by Charles Haskell and Elizabeth McKnight of New Century Conservation Trust, a non-profit environmental education organization in Maine, and sponsored in part by the Theodore Roosevelt Association, the American Museum of Natural History, and the National Wildlife Federation. This expedition consisted of a total of