Clearwater river (river type) in the context of Brazilian Plateau

The Tocantins River (Portuguese: Rio Tocantins Portuguese pronunciation: [ˈʁi.u tokɐ̃ˈtʃĩs, tu-], Parkatêjê: Pyti [pɨˈti]) is a river in Brazil, the central fluvial artery of the country. In the Tupi language, its name means "toucan's beak" (Tukã for "toucan" and Ti for "beak"). It runs from south to north for about 2,450 km (1,520 mi). While sometimes included in definitions of the Amazon basin, the Tocantins is not a branch of the Amazon River, since its waters flow into the Atlantic Ocean via an eastern channel of the Amazon Delta, alongside those of the Amazon proper. It flows through four Brazilian states (Goiás, Tocantins, Maranhão, and Pará) and gives its name to one of Brazil's newest states, formed in 1988 from what was until then the northern portion of Goiás.

The Tocantins is one of the largest clearwater rivers in South America.

A blackwater river is a type of river with a slow-moving channel flowing through forested swamps or wetlands. Most major blackwater rivers are in the Amazon Basin and the Southern United States. The term is used in fluvial studies, geology, geography, ecology, and biology. Not all dark rivers are blackwater in that technical sense. Some rivers in temperate regions, which drain or flow through areas of dark black loam, are simply black due to the color of the soil; these rivers are black mud rivers. There are also black mud estuaries.

Blackwater rivers are lower in nutrients than whitewater rivers and have ionic concentrations higher than rainwater. The unique conditions lead to flora and fauna that differ from both whitewater and clearwater rivers. The classification of Amazonian rivers into black, clear, and whitewater was first proposed by Alfred Russel Wallace in 1853 based on water colour, but the types were more clearly defined by chemistry and physics by Harald Sioli [de] from the 1950s to the 1980s. Although many Amazonian rivers fall clearly into one of these categories, others show a mix of characteristics and may vary depending on season and flood levels.

The Xingu River (/ʃɪŋˈɡuː/, shing-GOO; Portuguese: Rio Xingu [ˈʁi.u ʃĩˈɡu]; Mẽbêngôkre: Byti [bɯˈti]) is a 1,640 km (1,020 mi) river in north Brazil. It is a southeast tributary of the Amazon River and one of the largest clearwater rivers in the Amazon basin, accounting for about 5% of its water.

The Tapajós (Portuguese: Rio Tapajós [ˈhi.u tapaˈʒɔs]) 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 2,080 km (1,290 mi) long. Prior to a drastic increase in illegal gold mining and consequent soil erosion it was one of the largest clearwater rivers and currently is an anthropogenic whitewater river, accounting for about 6% of the water in the Amazon basin.