The Amazonian Manatee (Trichechus inunguis) is a species of manatee that lives in the Amazon Basin in Brazil, Peru, Colombia and Ecuador. It has thin, wrinkled brownish or gray colored skin, with fine hairs scattered over its body and a white chest patch. It is the smallest of the three extant species of manatee.

The Amazonian manatee is the only sirenian that lives exclusively in freshwater habitat. The species relies on changes in the peripheral circulation for its primary mechanism for thermoregulation by using sphincters to deflect blood flow from areas of the body in close contact with water. They also rely on subcutaneous fat to reduce heat loss.

Manatees have nostrils, not blowholes like other aquatic mammals, which close when underwater to keep water out and open when above water to breathe. Although manatees can remain under water for extended periods, surfacing for air about every five minutes is common. The longest documented submergence of an Amazonian manatee in captivity is 14 minutes.

Manatees make seasonal movements synchronized with the flood regime of the Amazon Basin. They are found in flooded forests and meadows during the flood season, when food is abundant. The Amazonian manatee has the smallest degree of rostral deflection (25° to 41°) among sirenians, an adaptation to feed closer to the water surface. It is both nocturnal and diurnal and lives its life almost entirely underwater. Only its nostrils protrude from the surface of the water while it searches river and lake bottoms for vegetation.

The Amazonian and West Indian manatees are the only manatees known to vocalize. They have been observed vocalizing alone and with others, particularly between cows and their calves.

The manatees themselves feed on a variety of aquatic macrophytes, including aroids (especially Pistia, aka "water lettuce"), grasses, bladderworts, hornworts, water lilies, and particularly, water hyacinths. They are also known to eat palm fruits that fall into the water. Maintaining a herbivorous diet, the manatee has a similar post-gastric digestive process to that of the horse. The manatee consumes approximately 8% of its body weight in food per day.

During the July–August dry season when water levels begin to fall, some populations become restricted to the deep parts of large lakes, where they often remain until the end of the dry season in March. They are thought to fast during this period, their large fat reserves and low metabolic

As of 1977 the population count of the Amazonian manatee was estimated to be around 10,000. As of now the total population count is undetermined, however the population trend seems to be decreasing. They are mainly distributed throughout the Amazon River Basin in northern South America, ranging from the Marajó Islands in Brazil through Colombia, Peru, and Ecuador. They are occasionally found overlapping with the West Indian manatee along the coasts of Brazil.

Amazonian manatees occur through most of the Amazon River drainage, from the headwaters, in Colombia, Ecuador and Peru to the mouth of the Amazon (close to the Marajó Island) in Brazil over an estimated seven million square kilometers. However, their distribution is patchy, concentrating in areas of nutrient-rich flooded forest, which covers around 300,000 km2 They also inhabit environments in lowland tropical areas below 300 m asl, where there is large production of aquatic and semi-aquatic plants; they are also found in calm, shallow waters, away from human settlements

The Amazonian manatee is completely aquatic and never leaves the water. It is the only manatee to occur exclusively in freshwater environments. The Amazonian manatee favors backwater lakes, oxbows, and lagoons with deep connections to large rivers and abundant aquatic vegetation They are mainly solitary but sometimes they will gather in small groups consisting of up to eight individuals. They engage in long seasonal movements, moving from flooded areas during the wet season to deep water-bodies during the dry season

Natural predators include jaguars, sharks, and crocodiles.