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2 regular, containing 5% rotenone were applied to the Green River and its tributaries between September 4th and 8th, 1962. The section of the Green River treated extended from above Big Piney, Wyoming to 10 miles above the present site of Flaming Gorge Dam, a distance of approximately 225 miles. To prevent destruction of fish and aquatic invertebrates in Dino- saur National Monument, 50 miles below the last rotenone application station, a detoxification station was established 12 miles above the Monument at Brown's Park Bridge. Approximately 17,160 pounds of pot- assium permanganate were dispensed from this station to detoxify the rotenone. Person}zel monitoring the river during the project felt that the detoxification was largely successful (Binns et al., 1963). Park rangers patrolling the river in the Monument during and shortly after the fish control project, however,eaw many dead and distressed fish. Whether these sightings indicated a passage of rotenone into the Monu- ment or the drifting of disabled fish into the Monument from above was not known. In either case it seems certain that the rotenone application re- sulted in a nearly complete kill of fish and bottom organisms at least as far as Brown's Park Bridge. Binns (1965) reported a severe reduction in standing crop of bottom organisms in the river above the dam site following the rotenone application. Populations of bottom organisms re- covered quickly the following :2 years, and some groups, such as Chiro- nomidae, recovered before others. The web-spinning caddis, Hydropsyche, was slow to re-establish itself throughout the river above the dam (Binns, 1965).