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, . T Background In response to a request from Mr. Bob Williams of the Upper Colorado Regional Office, a backwater habitat mapping study of the Green River in Utah was designed and implemented. The present study design was based on a pilot study conducted in 1986 to determine the feasibililty of using remote sensing and a Geographic Information System (GIS) to map backwater habitat (pucherelli et al. 1987). An environmental study involving the U. S. Bureau of Reclamation (BR) and the U. S. Fish and Wildlife Service (FWS) was initiated in 1986 in response to the proposed upgrade of Flaming Gorge Dam for the generation of additional hydro-electric power. The environmental study was designed to increase the understanding of the physical and biological requirements of the Colorado squawfish (Ptychocheilus lucius), an endangered fish species endemic to the Colorado River system. The Endangered Species Act of 1973 (Public Law 93-205) charges federal agencies to consider the needs of listed species, consult with FWS, and produce biological opinions relative to the impacts of planned projects. Information gained from these studies will enable the FWS to issue a biological opinion concering the operation of Flaming Gorge Dam. Following the installation of Flaming Gorge Dam the abundance of native fish species, including the Colorado squawfish, has decreased. Based on extensive studies (Tyus et al. 1987, Tyus and McAda 1984), the FWS has concluded that backwaters in the Green River are important nursery habitat for young-of-the-year Colorado squawfish. It is believed that maximizing backwater habitat in the Green River during the summer season may increase the survival rate of Colorado squawfish young-of-the-year. This study examines the relationship between flow (cfs) and number and area of backwaters on five sites in the Green River in Utah. Large scale aerial photography was obtained of each site for seven different flows. Aerial photographs were interpreted and incorporated into a digital data base. Tabular summaries and computer generated map plots were produced for each site. In addition, a field study was conducted to verify results and incorporate ground measurements of specific reference backwaters into the study. The objective of this study was to establish a data base that will allow determination of optimum Green River flows for backwater formation during the summer season. Methodology Five study sites were subjectively selected by the FWS and BR in areas known to contain important backwater habitat for Colorado squawfish young-of-the-year. Site locations are indicated in Figure 1 - Location Map, and are described as follows: Site Approximate River Mile Length (miles) Island Park Jensen Ouray Sand Wash Mineral Bottom 328.5 - 310.0 - 261.5 - 225.5 - 51. 0 - 334.5 303.0 251.5 222.5 57.0 6 7 10 3 6