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increased in number and distribution. There are two problems common to all man's development in Colorado: dewater- ing and channelization. During times of drought there is not enough water in the state for all uses. During times of flood there is usually too much, at least in terms of modern civilization. The native fish species are adapted to Colorado's extreme flow fluctuations. Man's constructions often are not. To assure adequate water supplies for cities, agriculture and business, reservoirs have been built to store water for future use. The stream or river reach upstream of a dam is periodically inundated with standing water and fish requiring flowing water are eliminated. Species which must migrate through the area during spawn- ing runs are stopped at the dam face and eventually may be eliminated. Water released from reservoirs is often drawn from the bottom of reservoirs. If the im- poundment is deep enough, the temperatures of the water is cold, even in the warmest summer months and, these coldwater releases eliminate warmwater fish from river reaches downstream of the dam. Two general types of water diversions impact Colorado fish populations. First, water is often diverted from one river basin to another drainage. Thousands of acre-feet of water are diverted from the west slope of the Continental Divide to supply the water needs of east slope cities. Natural water flow regimes are disrupted and species that need high spring flows to reproduce may be prohibited from spawning successfully. Secondly, water is also diverted from waterways for irrigation purposes and streams are often com- pletely dewatered resulting in loss of downstream flowing water habitat. In many waters a series of diversion dams may be used to remove any irrigation return flows or surfacing groundwater for a stream length of several miles. Species not able to withstand extensive dewater- ing are eliminated. Transmountain water diversions have altered the flow regimes of the Arkansas and South Platte rivers. Prior to the modern colonization of Colorado begin- ning in the 1860's, the mainstem South Platte along the eastern edge of the state periodically dried completely in the fall and winter months. Only fish that could withstand such arid conditions would have been able to inhabit the South Platte in this part of the river. Since the advent of the transmountain diversions, the South Platte on the eastern plains is no longer intermittent in nature, but flows year- round. More species of fish are able to in- habit this river reach now than in the past. The Fryingpan-Arkansas project diverts water from the west side of the Continen- tal Divide to the Arkansas River. Year- round flows in the Arkansas are likely to be higher, a factor which impacts the suc- cess or failure of a given species in main- taining viable populations. Many streams and rivers have been channelized to contain rivers within stream beds during periods of excess flow. Waterways are also channelized to prevent them from naturally altering stream beds, endangering man's highways, railroads, buildings, and other property. Miles of rivers and streams have been channelized and in most cases when a stream bed is channelized, the meandering curves, undercut banks, pools and streamside vegetation are removed. Water will be warmer, flow velocities faster, and depths shallower. Species not able to tolerate such conditions disappear. Introduction of Fish Species Through Stocking Not only has the physical habitat of Col- orado's waters been extensively altered, but biological conditions have been changed as well. Since the mid-1880's, man has been stocking native and exotic species throughout the state. The object of the stocking programs have been to in- crease fishing opportunity. Only a few species of fish that anglers prefer, two species of catfish, the orangespotted sun- fish, the green sunfish, and cutthroat trout were native in the state. Since that time, many species have been stocked through- out the state. A list of fish introduced to the state exceeds the scope of this book. Wiltzius (1982) outlined the known intro- duction of fish to Colorado and not only were species such as trout and bass desired by anglers stocked, but other species were accidently introduced. Fish culturists of the time were not in the prac- tice of sorting out extraneous species which may have gained access to their rearing ponds. Consequently, various min- nows, suckers, and others have been transferred from other drainage basins and states. Colorado's Little Fish