The Rio Paraíba do Sul is one of the most significant river systems in southeastern Brazil, flowing through the states of São Paulo, Minas Gerais, and Rio de Janeiro before emptying into the Atlantic Ocean. Cutting through a depressed tectonic valley corridor between the Serra do Mar and Serra da Mantiqueira mountain ranges, the river drains a vast basin that supports a remarkable diversity of aquatic life. As the largest river system partially crossing Rio de Janeiro territory, it winds through a landscape shaped by geology, agriculture, and dense human settlement — a river of great ecological importance and considerable fishing heritage. The basin hosts just over 100 native fish species, with roughly 40% of those species found nowhere else on Earth, making it a uniquely biodiverse fishery despite the pressures it faces.