The Amazonian manatee (Trichechus inunguis) is a species of manatee of the order Sirenia. It is found living in the freshwater habitats of the Amazon Basin in Brazil, Peru, Colombia and Ecuador. Its color is grey, but sometimes appears to be a brownish grey. It has thin, wrinkled skin, and is almost hairless, but has "whiskers" around its mouth. It also has a distinct white breast patch, with fine hairs scattered over its body. It lacks significant predation, other than being occasionally hunted by humans, usually with harpoons. The manatees themselves feed on a variety of aquatic macrophytes, including aroids, grasses, bladderwarts, hornworts, water lilies, and particularly, water hyacinths. 
An almost unique feature (amongst mammals) of the manatee is the constant replacement of molar teeth; new teeth enter at the back of the jaw and replace old and worn teeth at the front. The order's closest relatives, the elephants, also have teeth that get replaced, but have only a limited set of these replacement teeth.
The Amazonian manatee is the second-smallest species of manatee after the recently discovered dwarf manatee. It may reach a length of 2.8 m (9.2 ft). Females are typically larger than males, and can weigh 360 to 540 kg (790 to 1,190 lb). Unlike the West Indian manatee, it lacks nails on the end of most flippers.
Recently, a closely related, but far smaller species, the dwarf manatee (Trichechus pygmaeus), has been described from Brazil by Marc van Roosmalen. Called the peixe-boi anão in Brazilian Portuguese, it is about 130 cm (4.3 ft) long and lives in fast-flowing streams. Its validity has later been questioned, with some believing it to be an immature Amazonian manatee.
It is the only sirenian that exclusively lives in freshwater habitat. Amazonian manatees rely 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 ocean. They also rely on subcutaneous fat to reduce heat loss. Amazonian manatees (and manatees in general) were also found to be able to make long dives relative to other marine animals (up to 16 minutes in length), however these animals were restrained and when retested on free-diving individuals, the results showed less long-term diving (from 5 seconds to 10 minutes) dependent upon metabolic factors. Another unique feature to the Amazonian Manatee, as well as the Florida Manatee, is vocalization. Both species have been seen to vocalize both alone and to each other, particularly between cows and their calves. The Amazonian manatee is a seasonal breeder with a gestational period of 12-14 months and a prolonged calving period. Most births take place between December and July, with about 63% between February and May, during a time of rising river levels in their native region.
The IUCN red list ranks the Amazonian manatee as vulnerable. Current population declines are primarily a result of hunting, as well as calf mortality, climate change, and habitat loss. However, due to their murky water habitat it is difficult to gain accurate population estimates.
Hunting remains the largest problem and continues in much of its range, even within reserves. In 1986, it was estimated that the hunting levels in Ecuador were unsustainable and it would be gone from this country within 10-15 years. While hunting still occurs, an increasing risk to its continued survival in Ecuador is now believed to be the risk of oil spills. The oil exploration also means an increase in boat traffic on the rivers.
- Shoshani, J. (2005). Wilson, D. E.; Reeder, D. M, eds. Mammal Species of the World (3rd ed.). Johns Hopkins University Press. p. 93. ISBN 978-0-8018-8221-0. OCLC 62265494.
- Marmontel, M. (2008). Trichechus inunguis. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 29 December 2008.
- conserve nature manatee site
- Trichechus inunguis Sandra L. Husar Mammalian Species , No. 72, Trichechus inunguis (Jun. 15, 1977), pp. 1-4 Published by: American Society of Mammalogists Article Stable URL: http://www.jstor.org/stable/3503928
- Ecology, Distribution, Harvest, and Conservation of the Amazonian Manatee Trichechus inunguis in Ecuador Robert M. Timm, Luis Albuja V. and Barbara L. Clauson Biotropica , Vol. 18, No. 2 (Jun., 1986), pp. 150-156 Published by: The Association for Tropical Biology and Conservation Article Stable URL: http://www.jstor.org/stable/2388757
- van Roosmalen, M. G. M. A new species of living manatee from the Amazon.. Accessed on March 16, 2008.
- Trials of a Primatologist. - smithsonianmag.com. Accessed March 16, 2008.
- Amaral R.S., V.M.F da Silvia, and F.C.W Rosas. 2010. Body weight/length relationship and mass estimation using morphometric measurements in Amazonian manatees Trichechus inunguis Mammalia: Sirenia. Marine Biodiversity Records. 3:e105-e109.
- Gallican G.J., R.C. Best, and J.W. Kanwisher. 1982. Temperature regulation in the amazonian manatee trichechus inunguis. Physiological zoology The university of chicago press 255-262.
- Metabolism and Respiration of the Amazonian Manatee (Trichechus inunguis) G. J. Gallivan and R. C. Best Physiological Zoology , Vol. 53, No. 3 (Jul., 1980), pp. 245-253 Published by: The University of Chicago Press Article Stable URL: http://www.jstor.org/stable/30155787
- Evoked Brain Potentials Demonstrate Hearing in a Manatee (Trichechus inunguis) Theodore H. Bullock, Daryl P. Domning and Robin C. Best Journal of Mammalogy , Vol. 61, No. 1 (Feb., 1980), pp. 130-133 Published by: American Society of Mammalogists Article Stable URL: http://www.jstor.org/stable/1379969
- Seasonal Breeding in the Amazonian Manatee, Trichechus inunguis (Mammalia: Sirenia) Robin C. Best Biotropica , Vol. 14, No. 1 (Mar., 1982), pp. 76-78 Published by: The Association for Tropical Biology and Conservation Article Stable URL: http://www.jstor.org/stable/2387764
- Ecology, Distribution, Harvest, and Conservation of the Amazonian Manatee Trichechus inunguis in Ecuador. Robert M. Timm, Luis Albuja V. and Barbara L. Clauson. Biotropica , Vol. 18, No. 2 (Jun., 1986), pp. 150-156. Published by: The Association for Tropical Biology and Conservation. Article Stable URL: http://www.jstor.org/stable/2388757
- Multiple new species of large, living mammals (part III) - Tetrapod zoology. Accessed March 16, 2008.