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PREFACE This document is the report for Study #18-11 of the Five Year Flaming Gorge Research Program - FY'94, which is part of the Recovery Implementation Program for Endangered Fish Species in the Upper Colorado River Basin. The report synthesizes winter investigations from the upper basin with literature on winter conditions for native fishes, and identifies additional research for developing flow recommendations for Flaming Gorge Dam. An annotated bibliography of literature on winter investigations in rivers is presented as a supplement to this report. There is little information on winter ice processes in Large rivers regulated by hydropower dams. Some investigators have modeled projected effects of proposed projects, but none have validated conditions before and after construction. Other investigators have used models to predict ice processes resulting from existing facilities. Many relationships associated with physical ice processes and fluctuating flows have been described mathematically, and can be applied to the Green River. Few investigations have related ice processes to biological effects, particularly in regulated rivers. Reactions by primary producers, macroinvertebrates, and fish in small streams have been described, but there is little information from medium to large rivers. The paucity of information is especially notable for native fishes, particularly endangered species. This report merely scratches the surface of the complex and intricate subject of ice processes in rivers. The subject is particularly interesting in its application to a regulated river--the Green River-and merits particular attention because of the presence of endangered fishes. This document (Literature Synthesis) should be considered the first of three phases to comprehensively address the question of winter conditions in this regulated river. A second phase (Model Development) should be implemented shortly to assimilate hydrological, climatological, and geomorphological data for incorporation into existing models and mathematical relationships on ice processes and fluctuating flows. Models derived should be validated in the third phase (Model Validation), to provide predictive capability in management of Flaming Gorge Dam. ii