These data were compiled to explore the foraging ecology of Rainbow Trout (Oncorhynchus mykiss) in the Colorado River, Grand Canyon, Arizona. These data represent samples characterizing the availability of drifting invertebrate prey (hereafter, drift) and use of these invertebrate prey by rainbow trout determined by gut samples (hereafter, diets). Drift and diet sampling occurred in five distinct reaches downstream of Glen Canyon Dam (river kilometer (rkm) from the dam): (I) rkm 16.3-21.7; (II) rkm 52.8-58.3; (III) rkm 86.6-91.9; (IV) rkm 122.0-123.6; and (V) rkm 127.1-129.6. Samples were taken on 12 trips in April, July, September and January from April 2012 through January 2015. The aquatic prey base consists of 5 primary taxa; two small aquatic Diptera: black flies (Simuliium sp.) and midges (family Chironomidae), an amphipod crustacean (Gammarus lacustris), New Zealand mudsnail (Potamopyrgus antipodarum), and aquatic worms (Tubificidae and Lumbriculidae). The U.S. Geological Survey collected and processed 784 individual drift samples and 1,028 diet samples following the methods described in Kennedy et al. (2014). To analyze these data, we developed a Bayesian discrete choice model, the structure of which is described in Dodrill et al. (Larger Work Citation). These data are compiled by sampling trip and reach. Additionally, a subset of invertebrates from each sample were measured to the nearest mm in length to characterize their size distribution.