A 22.7 m3s discharge, which is at least 150 times normal summer discharge, reduced the population of marked young-of-the-year trout by 96% in the 49-day interim between the June 1972 preflood and August 1972 postflood samples. Other year classes decreased, but less dramatically. Mortality for young-of-the-year between August 1972 and October 1972 was negligible. The standing crop of trout was reduced from 26.4 kg/hectare in June to 21.9 kg/hectare in August. Of the surviving trout, 28.3% moved out of the section in which they were marked. No fish was recovered more than 1,220 m from the section in which it was marked.