The Tapajós (Portuguese: Rio Tapajós [ˈʁi.u tɐpɐˈʒɔs]) is a river in Brazil. It runs through the Amazon Rainforest and is a major tributary of the Amazon River. When combined with the Juruena River, the Tapajós is approximately 1,200 mi (1,900 km) long. For most of its length it runs through Pará State, but the upper (southern) part forms the border between Pará and Amazonas State. The source is at the Juruena–Teles Pires river junction. The Tapajós River basin accounts for 6% of the water in the Amazon Basin, making it the fifth largest in the system.
From the lower Arinos River (a tributary of Juruena) to the Maranhão Grande falls are a more or less continuous series of formidable cataracts and rapids; but from the Maranhão Grande to the mouth of Tapajós, about 188 mi (303 km), the river can be navigated by large vessels.
For its last 100 mi (160 km) it is between 4 and 9 mi (6.4 and 14.5 km) wide and much of it very deep. The valley of the Tapajós is bordered on both sides by bluffs. They are from 300 to 400 ft (91 to 122 m) high along the lower river; but a few miles above Santarém, they retire from the eastern side and do not approach the Amazon floodplain until some miles below Santarém.
Tapajós is the name for a proposed new Brazilian state, which would consist of the western part of the current state of Pará. The proposal was defeated in a referendum in 2011 and by law cannot be revived until 2015. Although electors within the territory of the proposed state voted strongly in favor, the vote was strongly negative among the larger population in what would have remained of Pará.
The proposed capital would be Santarém. It would have a population of about 1.3 million and an area of 722,358 km², comprising 27 out of Para's 144 municipalities. As of 2011, its GDP of BR$ 6.4 billion constituted 11% of the total GDP of Pará. The planned Belo Monte Dam would be located within the territory of Tapajós.
The two most populous municipalities would be Santarém (population 294,774) and Altamira (population 105,030).
In a referendum held on December 11, 2011, the residents of the state of Pará were asked to vote on proposals to split the state into three parts: Tapajós in the west, Carajás in the southeast, and a rump Pará in the northeast. The proposal to create Tapajós was defeated by a margin of 66.1% to 33.9%. Voting was highly polarized regionally, with voters in the territory of the proposed new state voting strongly in favor while voters in the rump Pará voted strongly against. In particular, more than 90% of voters in Santarém voted in favor, while more than 90% of voters in Belém voted against. The mayor of Santarém, Maria do Carmo, vowed to continue efforts to create the new state.