Tapajós

The Tapajós is a significant river located in Brazil. It flows through the dense Amazon rainforest. This river serves as a major tributary to the Amazon River. When it combines with the Juruena River, it forms a very long system. The Tapajós river basin contains about 6% of the water in the Amazon basin. This volume makes it the fifth largest river system in that region.

The river's course spans several geographic areas. Most of its length runs through the state of Pará. However, its upper southern section forms a border between Pará and Amazonas State. The river begins at the junction of the Juruena and Teles Pires rivers. In its upper reaches, the river features many formidable cataracts and rapids. These occur from the lower Arinos River to the Maranhão Grande falls. Below the Maranhão Grande, the river becomes much wider and deeper. This allows large vessels to navigate the final portion toward the mouth. The valley is often bordered by high bluffs.

Historically, the Tapajós was a clearwater river. These rivers are characterized by low conductivity and low levels of dissolved solids. They are very clear and often have a greenish color. Because of this, people often called it the "blue river." However, the river is now considered an anthropogenic whitewater river. This means human activities have changed its natural state. Increased illegal gold mining has caused significant soil erosion. This process has changed the water from clear to a light brown color.

Illegal gold mining, performed by people known as garimpeiros, damages the ecosystem. Miners use excavators and dredging barges to search for gold. They suck up mud from the stream bed and the riparian buffer. This process involves deforesting the land, which causes further degradation. Miners dump an estimated 7 million tonnes of sediment into the river every year. This massive amount of sediment is a primary cause of the water's new color. The loss of the original clearwater state is a major environmental shift.

Another serious issue involves the use of mercury during gold purification. Miners use a technique called amalgamation to separate gold. They add mercury to a mixer based on how much gold they expect to find. This process is often done without protective equipment or safety regulations. During mixing, the mercury becomes fine particles and becomes more soluble. Microbes can then turn this mercury into a more toxic substance called methylmercury. This toxin enters the food chain through the fish.

The presence of mercury has severe impacts on local inhabitants. The Munduruku people live in the Tapajós valley, in an area called Mundurukânia. They face serious health risks from eating contaminated fish. Mercury poisoning can lead to psychiatric disorders and visual disturbances. It can also cause infertility. This pollution is steadily degrading the ancestral lands of the Munduruku. The environmental and social costs of these mining practices are very high.

Biodiversity in the Tapajós basin is remarkably high. There are about 325 known fish species in the basin. This includes 65 endemic species, which live nowhere else on Earth. Scientists believe there may eventually be more than 500 recognized species. However, many species are currently threatened by proposed hydroelectric projects. A series of planned dams would create a continuous chain of waterways. These dams would use locks to eliminate the river's natural rapids and waterfalls.

Several large dam projects are being discussed for the river. The São Luiz do Tapajós Dam is one of the largest proposed projects. Its environmental licensing is currently suspended by IBAMA. This suspension is due to expected impacts on indigenous and river communities. The dam would flood parts of the Sawré Muybu Indigenous Territory. Another plan is the Jatobá Hydroelectric Power Plant, which would produce 2,338 MW. The Chacorão Dam is also controversial because it would flood Munduruku territory. These projects aim to turn the river into a waterway for transporting soybeans.