The forage fish assemblage of the Brazos River was sampled at one location above and four locations below Possum Kingdom Reservoir each month for one year. A total of 13,936 individuals representing 18 species, 14 genera and five families were collected. Five of these species,Notropis stramineus, Notropis atherinoides, Hybognathus placitus, Hybopsis aestivalis and Cyprinodon rubrofluviatiliswere found only upstream from Possum Kingdom Reservoir.Hybognatus placitusaccounted for 45% of fish captured at the upstream site. In contrast, nine species were collected exclusively in the tailwaters, includingEtheostoma spectabile, Percina sciera, Campostoma anomalum, Notropis venustus, Pimephales notatus, Labidesthes sicculusandFundulus notatus. Only four species were obtained at all five stations—Gambusia affinis, Menidia beryllina, Pimephales vigilax and Notropis lutrensis. N. lutrensiswas the most common tailwater species equalling 87.9% of the total downstream catch. Median species diversity indices ranged from 0.129 to 0.451 for the five stations, with the highest value at the upstream station. Coefficients of biotic similarity ranged from 0.20 to 0.62, with the upstream station clearly being the most dissimilar. These findings are discussed relative to environmental effects of hypolimnetic release of reservoir waters.