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the other from 39.1 to 43.3 between mid August and late September. On 29 October those same two fish were found at RM 21.6 and 29.7. On 22 April 1997, both pikeminnow were still in Yampa Canyon suggesting that both fish may have spent the winter low flow period in the canyon. Both fish were located in the vicinity ofthe spawning area during the first aerial contact on 24 July 1997, and both fish moved upstream afterward. On 13 August 199=1, both fish were still in Yampa Canyon. Passage Results from riffle cross sections were emphasized for concerns relatedto passage because this mesohabitat type is most likely to restrict movement during low flows. Selection of an average depth criterion is important because a small change in average depth can result in large differences in concomitant flows. The average depth for all riffles at a flow of93 cfs was 0.52 ft. The passage criterion used for adult pikeminnow was a maximum depth of at least 1.0 ft in at least one point on a cross section (Burdick 1996). The mean flow required for riffles to produce a maximum depth of 1.0 ft was 153 cfs. The potential for low flow barriers to postspawning migrant Colorado pikeminnow in the Yampa River was evaluated in 1997 by monitoring movement through two potential barriers, Cross Mountain Canyon (RM 58.8) and the Maybell Diversion (RM 89.4). Six-month transmitters were surgically implanted in five Colorado pikeminnow in the second week of May 1997 in the Yampa River between Government Bridge (RM 98.8 and Morgan Gulch (RM 103.7). Telemetry data was unable to identify passage barriers in 1997 because of extremely high base flows. Travel times indicated that individual fish only occupy the spawning area for a portion of the entire spawning period. Bestgen et al. (1997) estimated the duration of Colorado pikeminnow spawning in the Yampa River between 1990 and 1996 ranged from 24 and 38 days (mean = 29.5). Similarly, Tyus (1990) estimated pikeminnow spawning between 1981 and 1988 ranged from 31. and 39 days (mean = 35.6). The average time pikeminnow spent near the spawning area in 1997, a high baseflow year, was only 15.5 days. Although is likely that individual fish do not remain in the spawning area for the duration of the spawning period, what factors cause fish to leave the spawning area is not known. Although evidence suggested low flows in early to mid-July may be detrimental to spawning, it is unlikely the normal range of low baseflows are a factor in preventing passage of postspawning migrant adults. 12