Five rivers and 13 streams in the influence area of the Lajeado reservoir (upper-middle Tocantins River) were sampled in 5 expeditions. A total of 194 fish species were recorded and with the Characiformes and Siluriformes predominant, following the observed pattern for the Neotropical region. As expected, the families with greater richness were Characidae, Loricariidae and Cichlidae. Three species listed as Endangered were collected: Mylesinus paucisquamatus Jégu & Santos, 1988, Melanorivulus litteratus (Costa, 2010) and Paratrygon aiereba (Müller & Henle, 1841).