亚马逊海牛（Amazonian Manatee）是现存3种海牛中，体型最小的一种。其分布局限在亚马逊河流域的主要河道、支流与湖泊。在涨水期，亚马逊海牛会进入淹水的森林，而在较干燥的季节里，牠们则会退回深潭或大湖中。由于牠们害羞的天性与昏暗的栖息水域，人们对牠们的社会行为了解不多。在巴西，亚马逊海牛被称为“peixe-boi”（牛鱼），在其他西班牙语系国家则被称为“vaca marina”（意为“海牛”sea cow）或“manati”。种名inunguis的意思是“没有趾甲”，这是牠们不同于其他2种海牛的特点之一。

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, Bolivia, Colombia and Ecuador. 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 is also known as the Amazon manatee or sea cow.