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Red Shiner Notropis lutrensis Sand Shiner Notropis stramineus Fathead Minnow Pimephales promelas Redside Shiner Richardsonius balteatus Creek Chub Semotilus atromaculatus Longnose Sucker Catostomus catostomus White Sucker Catostomus commersoni Black Bullhead Ictalurus melas Channel catfish Ictalurus punctatus Rio Grande Killifish Fundulus zebrinus Mosquito Fish Gambusia affinis White Bass Morone chrysops Green Sunfish Lepomis cyanellus Bluegill Lepomis macrochirus Small Mouth Bass Micropterus dolomieui Large Mouth Bass Micropterus salmoides White Crappie Pomoxis annularis Black Crappie Pomoxis nigromaculatus Johnny Darter Etheostoma nigrum Yellow Perch Perca flavescens Walleye Stizostedion vitreum vitreum The upper Colorado region is divided into three major river basins: the Green, Colorado, and San Juan (Figure 1). Each is divided into three major aquatic system types or zones: the cold-water high mountain streams, the large, warm, turbid rivers; and an intermediate zone which is geographically as well as physically, chemically, and biologically intermediate between the former two. For the purpose of this report, these three river types will be labeled upper zone (headwaters), inter- mediate zone, and lower zone (large river channels). The upper zone is generally regarded as "trout water," for the cold temperatures, clear water, and high gradient streams, with rocky or gravelly substrate, result in ideal habitat for these cold water fish. Primary production is significant and is primarily found in the peri- phytic algae. Benthic invertebrate production is substantial and represents an important food source for resident salmonids which dom- inate the fish population. As the stream flows from the upper zone into the intermediate zone, the water warms, flow becomes greater, and increased quantities of suspended and dissolved solids are added. The waters of this zone are generally clear except during spring runoff and after heavy rains. Substrates are generally rocky with occasional expanses of sand, especially in small and medium-sized streams. Benthic invertebrates are generally very abundant in the rocky areas and scarce in the sandy regions. Salmonids are less common, and cyprinids and 4