The valley of the Paraíba do Sul ranges from the latitudes 20°26' and 23°39'S and the longitudes of 41° and 46°30'W and covers an area of about 57,000 km2 (22,000 sq mi) distributed over three states.

[2][3][4] The Paraíba do Sul basin is home to just above 100 native fish species with most in the families Loricariidae, Characidae and Trichomycteridae.

[6] As a consequence of flowing through one of the most densely populated and industrialised parts of Brazil, the Paraíba do Sul suffers from pollution.

[7][8][9] Studies of the native cichlid Geophagus brasiliensis have found that levels of some heavy metals exceed the limits set by the Brazilian Food Legislation.

[16] Other threatened species in the Paraíba do Sul basin are the bivalves Diplodon dunkerianus, D. expansus and D. fontaineanus, and the Hoge's side-necked turtle (Mesoclemmys hogei).