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the main rivers, has been lost as river bottoms were developed. Highway and railroad construction along the Colorado and Gunnison Rivers has resulted in miles of channelized stream banks. Kidd (1974) documented the disappearance of adult razorback suckers from a backwater located two miles downstream from DeBeque, Colorado when the area was channelized. Backwaters are used by many species during early life stages as nursery grounds and by adult fishes as resting and feeding stations. Unnatural water releases from the Curecanti Project on the Gunnison River have shifted the timing of high water periods and subsequent formation of backwaters. Instead of realizing peak flows in May and June, during reproductive periods, they now occur in December and January. Thus, the physical loss of habitat by modification of water tempera- tures and flows, and channelization of backwater areas has been a cause in the decline of bonytail chubs and razorback suckers. The introduction of non-native fishes into the Colorado River system has probably been occurring since the late 1800's when various trout species were released. As early as 1926, Platte River suckers (Catostomus commersoni and C. catostomus) were introduced near South Mesa Lake in the Colorado River headwaters. By 1942, the creek chub, Semotilus atromaculatus, and the fathead minnow, Pimphales promelas, were noticed in fish collections from the Colorado River at Hot Sulphur Springs, Colorado (Hubbs et al 1943). These releases preceded a deluge of introductions of Mississippian fishes. Bait minnows, like the redside shiner, Richardsoniusbalteatus, which are native to the Bonneville basin and the Columbia River drainage were released in the upper Green River in Wyoming. These and other minnows, suckers, and sunfish have quickly spread through the upper Colorado River system over the years until now the more adaptable forms (redside shiner) are ubiquitous. A recent survey - 8 -