Found in the main rivers of the Amazon Basin, the Amazonian manatee (Trichechus inunguis) is the largest aquatic freshwater mammal in South America. The objective of this study was to describe the ecological knowledge and uses of the Amazonian manatee in the Extractive Reserve Verde para Sempre, Porto de Moz, Brazilian Amazon. This study was conducted through semi-structured interviews, free interviews, participant observation and image capture. Thirty-one residents were interviewed in 21 communities, using snowball sampling method. The interviewees were previously identified by local informants and selected according to their level of knowledge of the species. We collected information on the morphology, behavioral characteristics and feeding habits of manatees, and on the uses of the species by communities. Our findings suggest three hypotheses on the biology of Amazonian manatee: 1-the existence of three phenotypic patterns based on skin color and amount of fat; 2-changes in land use by agriculture, livestock and the installation of the hydroelectric plant affect their spatial distribution and seasonal migration; 3-they show reproductive behavior during the rainy season, in a polygamous way as a strategy of maintenance and genetic variability of the species. One third of the interviewees learned of the prohibition of manatee poaching during the implementation of the reserve. Poaching and consumption of manatees are rare, and entanglement of calves in fishing nets is accidental. These results reinforce the interest of local ecological knowledge in understanding the biology of the Amazonian manatee and their contribution to the delimitation of protected areas.