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Elkhead Creek Aquatic Resource Report Miller Ecological Consultants, December 5, 1996 INTRODUCTION On 12-13 Sept. 1995 aquatic sampling was conducted at two sites on Elkhead Creek, Colorado for the purpose of documenting the distribution and abundance of aquatic vertebrate and invertebrate biota at sites upstream and downstream of Elkhead Reservoir. The findings reported here provide comparisons of fish distribution, abundance, and macroinvertebrate densities and diversities. This information can be used at a later date ' to assess the impacts of the proposed reservoir expansion. This study is one of several studies being conducted by the US Bureau of Reclamation/Colorado River Water Conservation ' District to gather information for use in the preparation of NEPA documents for the proposed enlargement of Elkhead Reservoir. ' Objectives ' The specific objective of this study was to collect current data on the aquatic environment to evaluate potential impacts from the enlargement of Elkhead Reservoir on the fishes in Elkhead Creek upstream and downstream of the existing reservoir. These data should be useful ' in conjunction with the habitat mapping data to address project impacts and potential mitigation measures. t MATERIALS AND METHODS Study Area Elkhead Creek is located in the Northwest region of Colorado with the area of concern flowing along the border of Routt and Moffat Counties (Figure 1). The site locations were selected to be representative of areas upstream and downstream of the existing reservoir that are most likely to be impacted by the proposed enlargement operations or facilities. Other site selection criteria include stream geomorphic characteristics and hydrologic regime. The selected sites each contain habitat and morphological characteristics that were typical of the respective stream reach. This study was conducted, and sites selected within the following river reaches: Elkhead Creek downstream of the existing reservoir and upstream of the Yampa River (Site 1); Elkhead Creek upstream of the existing reservoir and within the proposed inundation area (Site 2). The specific location of Site 1 is approximately 1.9 km downstream from the Elkhead Reservoir dam, and 9.4 km upstream from Highway 40 (Figure 2). Site 2 is located upstream of the existing reservoir and within the proposed inundation area. The lower boundary of Site 2 begins immediately upstream of the current County Road 76 bridge (Figure 3). These sites represent areas of greatest potential impact due to inundation or change in stream flow.