Rio Macaé is a river system in Rio de Janeiro State, Brazil, flowing through a diverse range of environments from its upper freshwater reaches down through an ecologically rich estuarine zone before meeting the Atlantic coast. The river supports a remarkable diversity of fish life — scientific surveys have recorded a total of 157 species of Teleostei throughout the Macaé River system, including 110 species across 44 families documented in the estuarine region alone. This biodiversity makes Rio Macaé one of the more species-rich river systems along the southeastern Brazilian coast, comparable to other major estuarine systems in the region that typically record between 100 and 200 species. Despite decades of environmental pressure from agricultural and urban development — much of the natural riparian vegetation along the estuary and adjacent freshwater areas has been replaced by pasture and crops — the estuary continues to serve as an important habitat for both coastal marine and continental freshwater fish fauna.