Rio Mucajaí is a significant tributary of the Rio Branco in the state of Roraima, Brazil, flowing through the heart of the Amazon basin in one of the most remote and ecologically rich regions of South America. The river drains portions of the Yanomami Indigenous Land and passes through dense Amazonian rainforest before joining the Rio Branco system. As part of the broader Rio Branco Basin, the Mucajaí supports a diverse array of Amazonian fish species and has historically served as an important fishing resource for indigenous communities and local populations alike. However, the river exists within a complex environmental context shaped by decades of gold mining activity that has had measurable impacts on the aquatic ecosystem and the fish that inhabit it.