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approximately RM 54) studies reviewed, only one data set showed n.onnative fishes to outnumber native fishes in the canyon reach of the Yampa River. In addition, three of four data sets representing both the lower and middle reaches of Yampa Canyon were characterized by a greater number of native than nonnative fishes. Fish collected in the lower reach of the Yampa River weie represented more by nonnative than native fishes (80%, four of five, of the data sets). All three data sets obtained between Deerlodge and Craig indicated that nonnative fishes were more abundant than native fishes. Another trend observed was the abundance of northern pike, Esox lucius, and smallmouth bass, Micropterus dolomieui, as sampled by the Interagency Standardized Monitoring Program above Yampa Canyon (McAda et al. 1994, and supplemental reports for years 1993 and 1994). Greatest numbers of both species in the Yampa River occurred simultaneously with the large water releases from Elkhead Reservoir in 1992 (Figure 11) and continued through 1993, prior to the higp runoff. Thus, it appears that discharges from Elkhead Reservoir, a 13,700 cfs reservoir on Elkhead Creek, are capable of dispensing significant numbers of nonnative fish in the Yampa River. The importance of native and nonnative fish distribution in the Yampa River to flows in not clear. In river reaches with the greatest range of depth and velocity (Yampa Canyon), native fishes are the dominant components. However, in areas above Yampa Canyon nonnative fish species are more abundant than native species. The influence of seasonally high runoff flows on the persistence of native fishes in Yampa Canyon is probably beneficial, however, the specific relationship in unknown. Comparison of Historical and Virgin Hydrographs Daily virgin flow estimates for the Yampa River were developed by Hydrosphere Resource Consultants, using methods described in their report, "Development of Estimated Daily Flows, Yampa River at Maybell" (Hydrosphere 1995a, Appendices 3 and 4). This set of estimates, hereafter referred to as virgin flows, was constructed by adding all estimated flow depletions back into the actual stream gage records for the Yampa River at Maybell, for the period 1950-82. Although we recognize a limitation in the mechanism used to generate these estimates, i.e. best estimates of depletions through time, we accept these values as the best estimate of virgin flows. The similarity of standard deviations within virgin and historical flows indicates that variation between these two data sets was nearly identical. In this regard, the estimated virgin flow regime provided a standard for comparison with historical flows. Historical flows are defined as actual, measured streamflows from 1950-82, which have been influenced by storage of small reservoirs in the Yampa River headwaters as well.as agricultural, municipal, and industrial diversions that have accumulated prior to, and during, this time period. 1.9