Tocantins River

The Tocantins River is a major fluvial artery in Brazil. This term describes a central water system that moves through a large area. The river's name comes from the Tupi language. It translates to "toucan's beak." The river is one of the largest clearwater rivers in South America. It flows from the south toward the north. While some people group it with the Amazon basin, it is not a branch of the Amazon River. Instead, its waters flow into the Atlantic Ocean through an eastern channel of the Amazon Delta.

The river travels through four Brazilian states. These are Goiás, Tocantins, Maranhão, and Pará. The river is so important that it gave its name to the state of Tocantins. This state was formed in 1988 from the northern part of Goiás. The river begins in the mountainous Pireneus district. Its western tributary, the Araguaia River, starts on the slopes of the Serra dos Caiapós. The Araguaia is a massive river itself. Its water volume is almost equal to that of the Tocantins.

The geography of the river basin is quite varied. The Tocantins and Araguaia flow through flat, broad valleys. These valleys consist of sand and clay. They sit below steep bluffs. These bluffs are the edges of sandstone plateaus. Over time, the rivers have eroded deep beds into this rock. In the lower reaches, the river acts as a natural barrier. It separates the Tocantins–Araguaia–Maranhão moist forests from the Xingu–Tocantins–Araguaia moist forests. This separation prevents plants and animals from moving easily between these two regions.

The river basin supports a rich variety of life. Many large aquatic mammals live here. These include the Amazonian manatee, the Araguaian river dolphin, and the tucuxi. You can also find large reptiles like the black caiman and the yellow-spotted river turtle. The fish population is very high. More than 350 fish species have been recorded in the basin. Over 175 of these are endemic species. Endemic means they are found nowhere else on Earth. The most common families are Characidae, Loricariidae, and Rivulidae.

Some of the most unique life is found in the dark. The São Domingos karst is a region in the upper basin. A karst is a landscape shaped by dissolving rocks like limestone. This area has more cavefish species than any other region in the Americas. One special fish is the Eigenmannia vicentespelaea. It is the only known cave-adapted knifefish in the area. It is also one of only two known non-catfish species living in South American mainland caves.

Humans have significantly altered the river through engineering. There are seven dams located along the river. These include the Serra da Mesa, Cana Brava, and São Salvador dams. The Peixe Angical, Luiz Eduardo Magalhães, and Estreito dams are also part of this system. The Tucuruí Dam is one of the largest in the world. Built in the early 1980s, it created a massive artificial lake. This dam flooded many former rapids and cataracts. It also changed the natural flow of the water.

These dams have impacted the river's ecology. Many fish species migrate along the Tocantins to spawn, or lay eggs. This movement has been restricted by the dams. The construction of the Tucuruí Dam caused a reduction in species richness in some parts of the river. To help with travel, a system of locks called Eclusas do Tucuruí was finished in 2010. These locks allow boats to move through the different water levels.

Finally, the river's mouth is a complex area. The Pará River is actually the lower reach of the Tocantins. Some people call it one of the mouths of the Amazon. However, the waters of the Amazon only reach the Pará through natural canals. These canals wrap around the large island of Marajó. They are not official outflow channels of the Amazon. The river remains a vital part of the South American landscape.