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5 RECOMMENDATIONS 1. To prevent ice breakup, or the transport and deposition of frazil ice in areas used by overwintering endangered fishes, large daily fluctuations at the Jensen gage should be avoided during extremely cold weather (mean daily air temperature about -7 'C or below) until surface ice has formed to approximately RM 310. During milder winters, when frazil ice production is reduced, less restrictive operations could occur without depositing frazil ice under the ice cover and without breaking up all but the thinnest ice covers past about RM 300 (Jensen Bridge). During the 1997 field study the mean daily flow at the Jensen gage was approximately 2,440 cfs and fluctuated daily between 1,700 and 3,500 cfs. These fluctuations did not deposit significant amounts of frazil under the ice cover and did not break up the ice cover downstream of RM 306. 2. Collect accurate hourly water temperatures at a number of locations throughout the study reach to improve calibration of the ice-process model and to test specific assumptions in the model (e.g., timing of the formation of frazil ice). To accomplish this, measurements accurate to the nearest 0.1 °C would be useful. Additional temperature information would provide information about the environmental conditions (such as supercooled water) that endangered fishes may encounter within the study reach. Collection of temperature data in other portions of the river could be used to investigate the distance to which Flaming Gorge Dam exerts a thermal influence on the river and the effects of fluctuating flows on temperature regimes. 3. Additional investigations should be conducted to characterize winter conditions in backwaters and other low-velocity habitats that may serve as overwintering areas for juvenile endangered fishes. Although such studies were conducted in backwater areas by Valdez and Cowdell (1999), the winters during those studies were unusually mild. Although main channel ice processes in the principal area used by overwintering native fishes do not appear to be greatly affected by fluctuating flows, shallower backwater areas used as nursery habitats by age-0 fish may be susceptible to inundation and desiccation. Consequently, the degree of use of these areas during winter and the physical conditions within such areas should be examined. -27-