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• ABSTRACT Distr--ibution-of-Macro invertebrates in the Green River Below Flaming Gorge Dam, 1963-1965 by --Wi-l-liam D. Pearson, Master of Science Utah State University, 1967 Major Professor: Dr. Robert H. Kramer Department: Wildlife Resources This study was undertaken to determine the effects of rotenone applied during a fish control operation in September 1962 and the in- stallation of Flaming Gorge Dam in November 1962 upon the distribution of invertebrates in the Green River. Since these two events, the • river has changed from a warm, turbid stream to a cold, clear trout. stream for about 45 miles below the dam. Totals of 234 bottom samples and 394 drift samples were collected between the dam and Ouray, Utah (166 miles below the dam). The species composition or the fauna above Carr Ranch was much simpler during 1964-65 tihan the reported pre-impoundment composition. Below Carr Ranch the species composition of the invertebrate fauna has changed little. Bottom- fauna densities were highest near the dam (max. 6347/ft.2) and de- creased with increasing distance below the dam. Population densi- ties below Carr Ranch (42.7 miles below the dam) appeared to be similar to reported pre-impoundment densities. Drift rates of Baetis nymphs and Simuliidae larvae were highest near the dam. Illumination, population-densit3'.of other organisms, and water temperature had