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The Amazon River and Flooded Forests ecoregion contains an extremely high number of freshwater animal species, including two species of freshwater dolphins. The ecoregion is characterized by extensive forested areas that become flooded during each rainy season. These "flooded forests" in the Amazon region are the most extensive of this habitat type in the entire world. The cycle of flooding, and the annual regeneration that it produces, represent a globally outstanding ecological phenomenon. The entire Amazon basin contains the largest number of freshwater fish species in the world, estimated at more than 3,000 species. This Global 200 ecoregion is made up of these terrestrial ecoregions: Iquitos varzea; Gurupa varzea; Rio Negro campinarana; Marajó varzea; Purus varzea; Monte Alegre varzea, Every year the Amazon River rises more than 30 feet (9 m) and floods surrounding forests. These rising waters replenish nutrients in floodplain areas and regenerate floodplain lakes, floating meadows, and other seasonal habitats. Freshwater fish move into these flooded forests and often feed on the fruits that drop from the trees.
The Amazon is the second longest river in the world (after the Nile), stretching 4,000 miles (6,400 kilometers). But it's the largest when it comes to volume. The Amazon contains 20 percent of the Earth's fresh water, which it carries from high up in the Andes Mountains to the Atlantic Ocean. Along the way, it picks up rich soil that flows into dozens of streams and small rivers. The Amazon Basin has two freshwater systems, the igapó (blackwater) and the varzea (whitewater). The varzea contains a large amount of minerals that fertilize land and help trees and other vegetation grow. Every year, fish, reptiles, and other aquatic animals migrate into these newly flooded habitats to feed and reproduce, then return to the main channels when the floodwaters recede. Terrestrial animals, such as a number of primate species, also rely on the floodplain forest habitats. The reproduction of many floodplain trees depends on the dispersal of their seeds by frugivorous (fruit-eating) animals, including several fish species. A few of the characteristic fishes of this ecoregion are the fruit-eating tambaqui, arawana, pirarucu, arapaima, dourada catfish; one of the world’s few surviving lungfishes, Lepidosiren paradoxa; and tucunaré. Mammals include the pink river dolphin or boto, gray river dolphin or tucuxi, manatee, and the rare uakari. The largest river turtle in South America, Podocnemis expansa, is also found here, as is the highly endangered black caiman.
In the flooded forests, selective logging of the kapok tree and virola is accelerating deforestation and wiping out populations of the above species over large regions. The open floodplains are threatened by conversion to cattle ranching and the widespread introduction of water buffalo, which are not native to the region and which cause damage to the shoreline vegetation and fish nursery areas. Overfishing, particularly of the largest species, is leading to declines in fish populations. Mercury pollution from gold mining in smaller streams may have long-term impacts. Because human population is increasing along the main rivers, untreated sewage is a growing problem. Roads built through the region open up access to previously remote areas and lead to erosion and increased use of the natural resources. Some dams exist already in the river basin and others are planned. These have the potential to block species movements and alter the flow of water.
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