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Tocantins River

The Tocantins River is a significant waterway in Brazil, stretching approximately 1,553 miles (2,500 kilometers) from its origin in Goiás, through Tocantins, Maranhão, and Pará, before merging with the Amazon River near Belém. The river is formed by the confluence of the Paraná and Maranhão rivers, and its basin features a range of habitats, including flat landscapes, flooded plains, and diverse aquatic environments. The region is renowned for its biodiversity, hosting an array of species, including 153 mammals, over 500 bird species, and more than 300 fish species, many of which are migratory.

Historically, the Tocantins has been inhabited for thousands of years, with indigenous tribes such as the Apinajé and Karajá residing along its banks. The river has also been influenced by human activities, notably the construction of large dams, such as the Tucuruí and Serra da Mesa, which have altered its natural flow and affected local fish populations. These changes, along with deforestation for agriculture and logging, have raised concerns about the ecological balance of the area. Efforts for conservation exist, but protection is limited, with only a few designated reserves safeguarding parts of the river’s ecosystem. Overall, the Tocantins River plays a crucial role in both the natural environment and the cultural landscape of the region.

Full Article

  • Category: Inland Aquatic Biomes.
  • Geographic Location: South America.
  • Summary: One of Brazil’s major rivers runs through the Cerrado and Amazon, connecting populations in central Brazil and bringing energy and sustainability to several native populations.

The Tocantins River rises in the state of Goiás in central Brazil and runs northward through different sedimentary basins for roughly 1,522 miles (2,450 kilometers) in the states of Tocantins, Maranhão, and Pará. It is formed by a main tributary known as the Araguaia River. At the end of its course, the Tocantins flows into the Pará River estuary near Belém. Tocantins means “toucan’s beak” in the Tupi Indigenous language.

The landscape drained by the river is relatively flat, with flooded plains; the banks of the river sometimes flood, creating a white-sand igapó forest. The soils are nutrient-rich in many areas, but other areas have low nutrient availability in the soil.

The basin of the Tocantins is formed by another important river, the Araguaia, and has an average discharge of 388,461 cubic feet (11,000 cubic meters) per second. The most common aquatic habitats in the Tocantins are the rapids and the falls, dominating the upper course; they are less common in the middle reaches but form an important habitat on the lower course, which is now largely inundated by the Tucuruí Reservoir.

Rocky and sandy islands and beaches are usually found in the middle course; clay islands dominate in the lower reaches. Floodplain lakes are less frequent along the Tocantins. October to April witness many incidents of rising water, with February (upper Tocantins) and March (middle and lower courses) experiencing high-water peaks. The Tocantins-Araguaia system experiences a low-water period from May to October, with the lowest water levels in September.

The Tocantins and its tributaries can be classified as clear, nutrient-poor, low-ion, and low-sediment-load rivers. In the 2020s, heavy anthropogenic interventions have changed this pattern. The lower Tocantins is influenced by both tidal cycles and the annual rise and fall of the main river, and it has many marginal lakes and numerous islands. This part of the river course is a complex and fragile ecosystem.

Floodplain lakes and seasonally inundated forests in tributaries of the Tocantins are key habitats for the maintenance of aquatic food webs.

Human Settlement

The history of human occupation in the region dates back 11,000 to 12,000 years, with the first evidence of human presence in the middle Tocantins. This period corresponds to the beginning of the Holocene. The period of Portuguese colonization started in 1625, when a group of Jesuit missionaries established the first settlement in the middle Tocantins. Later, Bandeirantes from São Paulo went through the entire region in search of gold and minerals, and pioneered commercial navigation along the river.

Several Indigenous tribes are in the region that belong to different cultures. The Apinajé and Karajá are the major Indigenous people living in the region, along with the Xerente, Javaé, Xambioá, and Krahô. These tribes live in the lands on the left bank of the Tocantins and the right bank of the Araguaia, in the north of Tocantins state.

Captain S. C. Bullock provided a vivid report on one expedition that took place in the spring of 1922 through the Tocantins-Araguaia rivers, describing the geography, climate, landscape, and human diversity. The expedition was mounted to confirm the navigability of the river and to search for minerals with economic value in the vicinity.

Biodiversity

The region of the Tocantins River is biologically rich. The eutrophic soils sustain a rich and diverse biota, with many unique species that are found only in this place in the world; that is, they are endemic here. The forests in the region are generally classified as tropical moist forests. Additionally, the zoological diversity is remarkable. A total of 153 species of mammals have been recorded, of which eight are primates, and 21 are rodents. Also noteworthy is bat diversity, with more than 90 species.

Many other eye-catching species can be found in the region, such as spectacled caimans (Caiman crocodilus), black caimans (Melanosuchus niger), the vulnerable yellow-spotted sideneck turtles (Podocnemis unifilis), the vulnerable Amazonian manatees (Trichechus inunguis), and two species of river dolphins (Inia geoffrensis and Sotalia fluviatilis), both of which are listed as endangered. In 2014, researchers identified a unique species of dolphin in the region, the Araguaian boto (Inia araguaiaensis), also known as the Araguaian river dolphin. Bird diversity is particularly high, with at least 527 known species, including toucans, hawks, and the marvelous scarlet macaw (Ara macao). However, fish diversity in the Tocantins is considered to be low by Amazonian standards.

Effects of Human Activity

Five large dams were constructed along the Tocantins River; in the 2020s, more than five major hydroelectric dams operate in the Tocantins basin. The two largest ones are Tucuruí and Serra da Mesa. With the construction of the Tucuruí Dam, the natural flow of the Tocantins changed, and the migratory fish movements became dependent on the controlled water flow of the hydroelectric dam. Long-distance migratory species, such as large catfish, were directly affected because their upstream movements were interrupted by the dam.

However, other migratory species whose life cycles are completed downstream from the dam were also adversely affected, probably due to separate reasons, but perhaps stemming from altered sediment loads, different patterns of riverbank exposure, and related changes in the flora communities downstream.

Despite helping with the development of the region, these dams have further negative effects. In the early 2000s, twenty years after the river flow-closure by the Tucuruí Dam, a substantial reduction in fish-species richness occurred in the mid-Tocantins River. The main factor explaining this reduction may be associated with the lack of transference of fish from downriver to upriver. In addition, there is further evidence that the changes in the river channel modified not only species composition but also the size distribution of fish along the middle Tocantins River. It is estimated that only 20 percent of the species are large after the dam’s closure.

There is active local fishery activity in the middle Tocantins, both professional and artisanal, with an interesting symbiosis between fishers and dolphins (Inia geoffrensis), which are trained to herd the fish against fences to be rewarded with some trapped fish. Fisheries on the mid-Tocantins have a seasonal pattern. Almost half of the total capture is concentrated from May to August. This fact could be explained by the low level of the Tocantins River in this period, in parallel with the increase in the density of fish assemblage and the presence of large beaches. Nonetheless, the closure of the Tucuruí Dam and others along the river also negatively influenced this activity.

The large commercial species have decreased in number and are qualitatively reduced in that area of the Tocantins. Although total species richness remained the same, changes in the fish community occurred in the long term, such as the dominance of predatory species. Fishers also noticed that the Tucuruí Reservoir has led to an unprecedented increase in the abundance, length, and weight of some migratory fish species upstream of the dam. However, immediately after the closure of the reservoir in 1984, catches in the lower Tocantins decreased by 65 percent in the two subsequent years. Climate change may impact the migratory patterns of some fish species as well and alter the mix of varieties of fish that thrive in the different segments of the river. In 2025, the Brazilian government advanced plans to blast and dredge sections of the Tocantins River, including rocky rapids, to create a year-round navigation channel for agricultural exports under the Araguaia–Tocantins waterway project. The proposal has generated controversy, with federal prosecutors, environmental groups, and local fishing communities raising concerns about potential impacts on river morphology, fish migration, biodiversity, and traditional livelihoods.

The Tocantins-Araguaia region is an agricultural frontier and one of the most deforested regions of Legal Amazonia. This region has been ravaged by fire, commercial logging, agriculture, and cattle raising, mainly following the roads. It is estimated that the Tocantins has lost about 50 percent of its forest cover. Although deforestation fuels the expansion of development frontiers, the selective slashing of inundated trees in floodplains and riparian forests may pose a direct threat to fisheries. These changes affect the discharge of the river and patterns of flow and depth all along its length. In early 2026, the Brazilian government revoked a federal decree that would have privatized navigation rights on the Tocantins River, following pressure from Indigenous organizations and environmental groups concerned about ecological and social impacts.

Conservation Efforts

There are more than five protected areas in the basin. The 26,063-acre (10,547-hectare) biological reserve of Águas Emendadas,  as well as Chapada dos Veadeiros National Park, protect the headwaters of the Tocantins River. The 1,388,732-acre (562,000-hectare) Araguaia National Park and adjacent Indigenous lands preserve the middle Araguaia  floodplains, whereas a small biological reserve north of Mocajuba preserves part of the lower Tocantins landscape.


Bibliography

“Brazil to Blast Amazon Tributary for Grains Shipping as Soy Frontier Advances.” The Straits Times, 4 Nov. 2025, www.straitstimes.com/world/Brazil-to-blast-Amazon-tributary-for-grains-shipping-as-soy-frontier-advances. Accessed 3 Mar. 2026.

Bullock, C. S. “Tocantins and Araguaya Rivers, Brazil.” Geographical Journal, vol. 63, no. 5, 1924.

Butler, Rhett Ayers. “New Dolphin Discovered in the Amazon Surprises Scientists.” Mongabay, 23 Jan. 2014, news.mongabay.com/2014/01/new-dolphin-discovered-in-the-amazon-surprises-scientists/. Accessed 3 Mar. 2026.

Costa, Marcos Heil, et al. “Effects of Large-Scale Changes in Land Cover on the Discharge of the Tocantins River, Southeastern Amazonia.” Journal of Hydrology, vol. 283, 2003.

Garavello, J. C., et al. “Ichthyofauna, Fish Supply, and Fishermen Activities on the Mid-Tocantins River, Maranhão State, Brazil.” Brazilian Journal of Biology, vol. 70, no. 3, 2010.

Likens, Gene E., editor. River Ecosystem Ecology. Academic Press, 2010.

Lima, Renato Correia, et al. “Identification of Fish Specimens of the Tocantins River, Brazil, Using DNA Barcoding.” Journal of Fish Biology, 29 Mar. 2024, doi:10.1111/jfb.15721. Accessed 3 Mar. 2026.

Ribeiro, Mauro César Lambert de Brito, et al. “Ecological Integrity and Fisheries Ecology of the Araguaia-Tocantins River Basin, Brazil.” Regulated Rivers: Research & Management, vol. 11, 1995.

Silverman, Helaine, and William Isbell, editors. Handbook of South American Archaeology. Springer, 2008.

“Tocantins-Araguaia River System (Brazil).” Latin America & Caribbean Geographic, 6 June 2022, lacgeo.com/tocantins-araguaia-river-system-brazil. Accessed 3 Mar. 2026.

Watts, Jonathan. “‘The River Won’: How Campaigners in Brazilian Amazon Stopped Privatisation of Waterway.” The Guardian, 27 Feb. 2026, www.theguardian.com/environment/2026/feb/27/the-river-won-how-campaigners-in-brazilian-amazon-stopped-privatisation-of-waterway. Accessed 10 Mar. 2026.

Full Article

  • Category: Inland Aquatic Biomes.
  • Geographic Location: South America.
  • Summary: One of Brazil’s major rivers runs through the Cerrado and Amazon, connecting populations in central Brazil and bringing energy and sustainability to several native populations.

The Tocantins River rises in the state of Goiás in central Brazil and runs northward through different sedimentary basins for roughly 1,522 miles (2,450 kilometers) in the states of Tocantins, Maranhão, and Pará. It is formed by a main tributary known as the Araguaia River. At the end of its course, the Tocantins flows into the Pará River estuary near Belém. Tocantins means “toucan’s beak” in the Tupi Indigenous language.

The landscape drained by the river is relatively flat, with flooded plains; the banks of the river sometimes flood, creating a white-sand igapó forest. The soils are nutrient-rich in many areas, but other areas have low nutrient availability in the soil.

The basin of the Tocantins is formed by another important river, the Araguaia, and has an average discharge of 388,461 cubic feet (11,000 cubic meters) per second. The most common aquatic habitats in the Tocantins are the rapids and the falls, dominating the upper course; they are less common in the middle reaches but form an important habitat on the lower course, which is now largely inundated by the Tucuruí Reservoir.

Rocky and sandy islands and beaches are usually found in the middle course; clay islands dominate in the lower reaches. Floodplain lakes are less frequent along the Tocantins. October to April witness many incidents of rising water, with February (upper Tocantins) and March (middle and lower courses) experiencing high-water peaks. The Tocantins-Araguaia system experiences a low-water period from May to October, with the lowest water levels in September.

The Tocantins and its tributaries can be classified as clear, nutrient-poor, low-ion, and low-sediment-load rivers. In the 2020s, heavy anthropogenic interventions have changed this pattern. The lower Tocantins is influenced by both tidal cycles and the annual rise and fall of the main river, and it has many marginal lakes and numerous islands. This part of the river course is a complex and fragile ecosystem.

Floodplain lakes and seasonally inundated forests in tributaries of the Tocantins are key habitats for the maintenance of aquatic food webs.

Human Settlement

The history of human occupation in the region dates back 11,000 to 12,000 years, with the first evidence of human presence in the middle Tocantins. This period corresponds to the beginning of the Holocene. The period of Portuguese colonization started in 1625, when a group of Jesuit missionaries established the first settlement in the middle Tocantins. Later, Bandeirantes from São Paulo went through the entire region in search of gold and minerals, and pioneered commercial navigation along the river.

Several Indigenous tribes are in the region that belong to different cultures. The Apinajé and Karajá are the major Indigenous people living in the region, along with the Xerente, Javaé, Xambioá, and Krahô. These tribes live in the lands on the left bank of the Tocantins and the right bank of the Araguaia, in the north of Tocantins state.

Captain S. C. Bullock provided a vivid report on one expedition that took place in the spring of 1922 through the Tocantins-Araguaia rivers, describing the geography, climate, landscape, and human diversity. The expedition was mounted to confirm the navigability of the river and to search for minerals with economic value in the vicinity.

Biodiversity

The region of the Tocantins River is biologically rich. The eutrophic soils sustain a rich and diverse biota, with many unique species that are found only in this place in the world; that is, they are endemic here. The forests in the region are generally classified as tropical moist forests. Additionally, the zoological diversity is remarkable. A total of 153 species of mammals have been recorded, of which eight are primates, and 21 are rodents. Also noteworthy is bat diversity, with more than 90 species.

Many other eye-catching species can be found in the region, such as spectacled caimans (Caiman crocodilus), black caimans (Melanosuchus niger), the vulnerable yellow-spotted sideneck turtles (Podocnemis unifilis), the vulnerable Amazonian manatees (Trichechus inunguis), and two species of river dolphins (Inia geoffrensis and Sotalia fluviatilis), both of which are listed as endangered. In 2014, researchers identified a unique species of dolphin in the region, the Araguaian boto (Inia araguaiaensis), also known as the Araguaian river dolphin. Bird diversity is particularly high, with at least 527 known species, including toucans, hawks, and the marvelous scarlet macaw (Ara macao). However, fish diversity in the Tocantins is considered to be low by Amazonian standards.

Effects of Human Activity

Five large dams were constructed along the Tocantins River; in the 2020s, more than five major hydroelectric dams operate in the Tocantins basin. The two largest ones are Tucuruí and Serra da Mesa. With the construction of the Tucuruí Dam, the natural flow of the Tocantins changed, and the migratory fish movements became dependent on the controlled water flow of the hydroelectric dam. Long-distance migratory species, such as large catfish, were directly affected because their upstream movements were interrupted by the dam.

However, other migratory species whose life cycles are completed downstream from the dam were also adversely affected, probably due to separate reasons, but perhaps stemming from altered sediment loads, different patterns of riverbank exposure, and related changes in the flora communities downstream.

Despite helping with the development of the region, these dams have further negative effects. In the early 2000s, twenty years after the river flow-closure by the Tucuruí Dam, a substantial reduction in fish-species richness occurred in the mid-Tocantins River. The main factor explaining this reduction may be associated with the lack of transference of fish from downriver to upriver. In addition, there is further evidence that the changes in the river channel modified not only species composition but also the size distribution of fish along the middle Tocantins River. It is estimated that only 20 percent of the species are large after the dam’s closure.

There is active local fishery activity in the middle Tocantins, both professional and artisanal, with an interesting symbiosis between fishers and dolphins (Inia geoffrensis), which are trained to herd the fish against fences to be rewarded with some trapped fish. Fisheries on the mid-Tocantins have a seasonal pattern. Almost half of the total capture is concentrated from May to August. This fact could be explained by the low level of the Tocantins River in this period, in parallel with the increase in the density of fish assemblage and the presence of large beaches. Nonetheless, the closure of the Tucuruí Dam and others along the river also negatively influenced this activity.

The large commercial species have decreased in number and are qualitatively reduced in that area of the Tocantins. Although total species richness remained the same, changes in the fish community occurred in the long term, such as the dominance of predatory species. Fishers also noticed that the Tucuruí Reservoir has led to an unprecedented increase in the abundance, length, and weight of some migratory fish species upstream of the dam. However, immediately after the closure of the reservoir in 1984, catches in the lower Tocantins decreased by 65 percent in the two subsequent years. Climate change may impact the migratory patterns of some fish species as well and alter the mix of varieties of fish that thrive in the different segments of the river. In 2025, the Brazilian government advanced plans to blast and dredge sections of the Tocantins River, including rocky rapids, to create a year-round navigation channel for agricultural exports under the Araguaia–Tocantins waterway project. The proposal has generated controversy, with federal prosecutors, environmental groups, and local fishing communities raising concerns about potential impacts on river morphology, fish migration, biodiversity, and traditional livelihoods.

The Tocantins-Araguaia region is an agricultural frontier and one of the most deforested regions of Legal Amazonia. This region has been ravaged by fire, commercial logging, agriculture, and cattle raising, mainly following the roads. It is estimated that the Tocantins has lost about 50 percent of its forest cover. Although deforestation fuels the expansion of development frontiers, the selective slashing of inundated trees in floodplains and riparian forests may pose a direct threat to fisheries. These changes affect the discharge of the river and patterns of flow and depth all along its length. In early 2026, the Brazilian government revoked a federal decree that would have privatized navigation rights on the Tocantins River, following pressure from Indigenous organizations and environmental groups concerned about ecological and social impacts.

Conservation Efforts

There are more than five protected areas in the basin. The 26,063-acre (10,547-hectare) biological reserve of Águas Emendadas,  as well as Chapada dos Veadeiros National Park, protect the headwaters of the Tocantins River. The 1,388,732-acre (562,000-hectare) Araguaia National Park and adjacent Indigenous lands preserve the middle Araguaia  floodplains, whereas a small biological reserve north of Mocajuba preserves part of the lower Tocantins landscape.


Bibliography

“Brazil to Blast Amazon Tributary for Grains Shipping as Soy Frontier Advances.” The Straits Times, 4 Nov. 2025, www.straitstimes.com/world/Brazil-to-blast-Amazon-tributary-for-grains-shipping-as-soy-frontier-advances. Accessed 3 Mar. 2026.

Bullock, C. S. “Tocantins and Araguaya Rivers, Brazil.” Geographical Journal, vol. 63, no. 5, 1924.

Butler, Rhett Ayers. “New Dolphin Discovered in the Amazon Surprises Scientists.” Mongabay, 23 Jan. 2014, news.mongabay.com/2014/01/new-dolphin-discovered-in-the-amazon-surprises-scientists/. Accessed 3 Mar. 2026.

Costa, Marcos Heil, et al. “Effects of Large-Scale Changes in Land Cover on the Discharge of the Tocantins River, Southeastern Amazonia.” Journal of Hydrology, vol. 283, 2003.

Garavello, J. C., et al. “Ichthyofauna, Fish Supply, and Fishermen Activities on the Mid-Tocantins River, Maranhão State, Brazil.” Brazilian Journal of Biology, vol. 70, no. 3, 2010.

Likens, Gene E., editor. River Ecosystem Ecology. Academic Press, 2010.

Lima, Renato Correia, et al. “Identification of Fish Specimens of the Tocantins River, Brazil, Using DNA Barcoding.” Journal of Fish Biology, 29 Mar. 2024, doi:10.1111/jfb.15721. Accessed 3 Mar. 2026.

Ribeiro, Mauro César Lambert de Brito, et al. “Ecological Integrity and Fisheries Ecology of the Araguaia-Tocantins River Basin, Brazil.” Regulated Rivers: Research & Management, vol. 11, 1995.

Silverman, Helaine, and William Isbell, editors. Handbook of South American Archaeology. Springer, 2008.

“Tocantins-Araguaia River System (Brazil).” Latin America & Caribbean Geographic, 6 June 2022, lacgeo.com/tocantins-araguaia-river-system-brazil. Accessed 3 Mar. 2026.

Watts, Jonathan. “‘The River Won’: How Campaigners in Brazilian Amazon Stopped Privatisation of Waterway.” The Guardian, 27 Feb. 2026, www.theguardian.com/environment/2026/feb/27/the-river-won-how-campaigners-in-brazilian-amazon-stopped-privatisation-of-waterway. Accessed 10 Mar. 2026.

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