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INTRODUCTION Escapement ofnon-native fish from Elkhead Reservoir has been identified as a potential impact to listed fish in the Yampa River. Fish escapement from the reservoir was included in the 2001 work plan for Elkhead Reservoir enlargement studies conducted by Miller Ecological Consultants, Inc. Miller and Laiho (1997) recommended study of escapement prior to the selecting an escapement control device. The potential cost of building and installing a flexible, Kevlar-like net, suspended in the water column to minimize fish escapement from Elkhead Reservoir is estimated near $1 million. It is presumed that annual operating and maintenance of this screen will also be significant. These potential-costs compel an evaluation offish escapement as apre-requisite task to justify this investment in both the recovery of the endangered Colorado River fishes and the reservoir sportfishery. Miller Ecological Consultants, Inc. collected aquatic resource information in fall of 1995 on Elkhead Creek for fish and macroinvertebrates (Miller and Rees 1996). Two sites were studied, one downstream of the reservoir and one upstream of the reservoir. The data provided baseline information for the stream aquatic resources downstream and upstream of Elkhead Reservoir. Results of this survey demonstrated the presence of small numbers black crappie and bluegill, and relatively abundant smallmouth bass in the creek near the dam outlet. Most bass were 30-95 mm in length with only four of 192 fish exceeding 100 mm. Colorado Division of Wildlife collected data on the reservoir fishery in 1999 (Bill Elmblad, CDOW personal communication). They sampled with electrofishing and gill nets. The results of that survey showed that approximately 80% of the fish captured were nonnative game species. Nonnative white sucker made up the largest segment of nongame fish (15%). No native fish were collected in the reservoir. The reservoir was again sampled in 2001 (Miller Ecological 2004), and results on relative abundance confirmed those of CDOW, showing smallmouth bass, black crappie and bluegill to be the most common species. Miller Ecological Consultants conducted a preliminary escapement study during the summer and fall of 2001 but due to the short runoff period, data were not collected during runoff (Miller Ecologica12004}. It was hypothesized that the potential for escapement is greatest during the snowmelt runoffperiod from May through June. This study provides results from monitoring escapement during runoff in 2003 and 2004. Elkhead Reservoir represents the largest reservoir in the Yampa Valley with potential and opportunities for warmwater fishing recreation. Due to its size, it offers considerable capacity to serve as a receiving water for nonnative gamefish species targeted for control and removal from the Yampa River. Relocation of adult gamefish from the river to the reservoir could potentially serve a net benefit of both reducing their impacts on native riverine fish populations (including the federally endangered fish species), and providing sportfishery potential in the reservoir. A habitat suitability rating projected for an enlarged Elkhead Reservoir based on a pattern judgement model using physical factors indicated suitable habitat for smallmouth and largemouth bass would remain low, similar to conditions at the existing reservoir (Bergersen and Martinez 2003). Despite the apparent biological limitations based on reservoir habitat modeling, the local populace regards this reservoir as a desirable fishery for these species. Interaction, with the local bass-fishing club demonstrated members were generally satisfied with the current productive capacity of the reservoir for producing desirable-sized bass (Tom Nesler, Colorado FINAL REPORT - Elkhead Reservoir Escapement, Project No.: 118 Page 1 Miller Ecological Consultants, Inc. May 20, 2005