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. DRAFT . observed. The top of the ice pack was first observed on Janlli'lry 31 at RM 315.9. At that time, large ice masses were jammed across the channel forming an extensive pond that backed water upstream for about 0.5 miles. Large pieces of floating ice were colliding wi th the top of the ice jam and were either stacked on top or were pulled underwater and transported downstream beneath the ice pack to a point where they became lodged. The noise created by these masses of ice moving beneath the ice pack was a very audible rumble. That point marked the beginning of continuous ice cover downstream well beyond the lower boundary of our study area. From RM 315.9 to 309.8 the river was covered with highly fractured and very unstable ice. At RM 309.8, consistent solid ice appeared along the shorelines with jam ice still prevalent over most of the channel. From RM 309.8 to RM 306.8, a mosaic of jam ice and solid ice existed, with solid ice becoming more typical progressively downstream. . . 3. Frazil ice. Extremely low air temperatures from late December, 1987 through mid February, 1988 resulted in supercooled river water conducive to the formation of large amounts of frazil or slush ice. Frazil ice was observed frequently in the upper region of the study area at Island and Rainbow Parks and between Split Mountain and Jensen. It was generally most prevalent in the early morning and became less apparent after about 1000 hours. During extended periods of subzero temperatures and with minimal solar radiation, frazil ice was present in the channel throughout the day. Several times in January, frazil ice development was so extensive that it filled the channel and appeared to be affecting water velocities. . . The aCCUImJlation of frazil ice under jam or solid ice was first noticed in January when holes were drilled through the ice to take microhabitat measurements at fish locations. At several locations between RM 308 and 312 columns of frazil ice 2 to 3 feet thick were encountered between the solid or jam surface ice and free water flowing on the bottom (Figure 3). Further evidence of extensive frazil ice aCCUImJlation was observed following breakup in the region between the Chew Bridge (RM 316.3) and the Dinosaur Quarry visitor Center (RM 306.8). Profiles of the ice column along the shoreline were exposed following breakup and transport of ice from the main channel. Observationsand measurements of these profiles showed aCCUImJlations of frazil ice ranging from 1 to 10 feet beneath the surface ice. . . 5.0 SUMMARY OF RADIOTAGGED FISH . A total of 40 fish were caught by electrofishing and implanted with radio- transmitters during the 2 years of this investigation, including 20 Colorado squawfish, 19 razorback suckers and 1 razorback sucker-flannelmouth sucker hybrid (Table 2). During the 2 year study, only of the three radiotagged fish were believed to have died; the carcus and radiotag of razorback GR61l0 was recovered in year 1 and the radiotags were recovered from squawfish and in year 2. These carcuses were not recovered. . A complete set of field data associated with the electrofishing effort as well as subsequent radiotracking information and habitat measurements have been submi t ted as a supplemental report to the BOR in Salt Lake City and the FWS/CRFP in Vernal Utah. 21 .