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abundant in reaches 3 and 4, where all pike and most pikeminnow were found. In upstream reaches 1 and 2 of Lodore Canyon, where mostly larger prey were found, all Colorado pikeminnow captured or sighted were 614 to 780 mm TL. Thus, size-structure of potential prey items and their habitat may affect the distribution and sizes of piscivorous fishes, particularly Colorado pikeminnow, in the Lodore Canyon reach of the Green River. Fish of any species and life stage were rare in deep, slow runs with sand substrate, presumably because they lacked substrate to support algal and invertebrate communities. This was particularly true in lower Browns Park, where substrate was almost exclusively shifting sand. Limited sampling in that reach suggested that the few brown trout and juvenile white suckers captured were associated with deep undercut banks and woody debris. Native catostomids were few and associated almost exclusively with scarce patches of cobble or waste concrete eroded from bank rip-rap. We feel reasonably confident that electrofishing sampling detected nearly all of the species in the main channel of the Green River in Lodore Canyon. Electrofishing was also a much better technique to detect the presence of relatively rare, large-bodied species such as Colorado pikeminnow and northern pike, compared to seining, which detected none of those taxa. With the exception of the few large eddies and pools greater than 3 m deep, electrofishing effectively sampled most of the habitat where Colorado pikeminnow were likely to occur. In contrast, our ability to effectively estimate the distribution and abundance of channel catfish by electrofishing was poor. We know this because channel catfish were rare in electrofishing samples in reaches 2 and 3 of Lodore Canyon but could be readily captured by angling. The diversity and abundance of hybrid suckers we encountered in this study was unexpected. Increased rates of hybridization maybe due in large part to relatively recent expansion of white suckers into the Green River upstream of the Yampa River. A single specimen ofthat-species was detected in a rotenone sample taken in September 1957 in the Green River in Browns Park, along with speckled dace, roundtail chub, flannelmouth sucker and a single chub tentatively identified as a bonytail (Nolting 1957). White sucker was not detected 31