<P> More than one - third of all known species in the world live in the Amazon rainforest, a giant tropical forest and river basin with an area that stretches more than 5,400,000 square kilometres (2,100,000 sq mi). It is the richest tropical forest in the world in terms of biodiversity . There are over 3,000 species of fish currently recognised in the Amazon basin, with more being discovered every year . In addition to the thousands of species of fish, the river supports crabs, algae, and turtles . </P> <P> Along with the Orinoco, the Amazon is one of the main habitats of the boto, also known as the Amazon river dolphin (Inia geoffrensis). It is the largest species of river dolphin, and it can grow to lengths of up to 2.6 metres (8 ft 6 in). The colour of its skin changes with age; young animals are gray, but become pink and then white as they mature . The dolphins use echolocation to navigate and hunt in the river's tricky depths . The boto is the subject of a legend in Brazil about a dolphin that turns into a man and seduces maidens by the riverside . </P> <P> The tucuxi (Sotalia fluviatilis), also a dolphin species, is found both in the rivers of the Amazon basin and in the coastal waters of South America . The Amazonian manatee (Trichechus inunguis), also known as "seacow", is found in the northern Amazon River basin and its tributaries . It is a mammal and a herbivore . Its population is limited to freshwater habitats, and, unlike other manatees, it does not venture into salt water . It is classified as vulnerable by the International Union for Conservation of Nature . </P> <P> The Amazon and its tributaries are the main habitat of the giant otter (Pteronura brasiliensis). It is a member of the weasel family and is the largest of its kind . Because of habitat destruction and hunting, its population has dramatically decreased . </P>

What country is the mouth of the amazon river in