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/ Y ` r -3- The manipulation of fish populations by chemical treatment is one of the most generally accepted techniques at the disposal of fisheries biologists. Properly administered rotenone toxicants have relatively short range effects on aquatic flora and fauna, are not cumulative, do not endanger homoiothermal species, and can be contained within specific habitat. Fish and Game Agencies in Utah and Wyoming are charged with the responsibility of providing a sport fishery where possible. This is particularly important in the semi-arid intermountain region. It is anticipated that fishing pressure on Flaming Gorge Reservoir will reach a magnitude never before encountered on waters in either state. The control of nongame species is an important initial step in the development and management of this large reservoir sport fishery. Initial estimates, based on conservative figures, anticipate that between 120,000 and 150,000 annual fishermen days will be spent on the waters of the Flaming Gorge Reservoir. B,y 1975, this use is expected to reach 185,000 to 228,000 fishermen days. These figures do not include fishermen use of the upper Green River proper and the Fontenelle Reservoir, both within the area covered by the project. During the years between approva_1 of the fish control project by the Federal Government and its consumation, a few individuals and groups mounted a campaign to block treatment of the river. This opposition contended that the chemical treatment constituted a threat to the survival of a few fish species indigenous to the Colorado River drainage. These species are the Colorado River squawfish, Ptychocheilus Lucius, the humpback sucker, Xyrauchen texanus, a form of chub closely associated with the roundtail and bonytail and sometimes identified as Gila cypha, the humpback chub. A11 of these species have been described as being specially adapted to swift water environments. It seemed probable to expect that the environmental changes resulting from impoundment would be responsible for any drastic reductions in swift water species. On this premise the use of rotenone would be largely academic. Long before treatment commenced investigations conducted by fisheries biologists of the Wyoming, Utah and Colorado Fish and Game Departments verified the existence of these fish in well established numbers on the mainstem of the river and several major tributaries outside the treatment area. Originally the treatment was to be coordinated with the closure of Flaming Gorge Dam in September, 1962 so as to confine toxicant to the impound- ment area. Late in the year of 1961 it became evident that construction of the dam would not be completed until sometime in November, 1962. Since rotenone would be less effective in the colder temperature prevalent during that time of year, the treatment had to take place earlier. A request was made of the Bureau of Reclamation to close the diversion tunnel at the time of the treatment and hold water behind the coffer dam for one or two days. This would provide time for rotenone to dissipate. The Bureau indicated that structural aspects of the diversion tunnel and coffer dam were such that this plan might cause damage and jeopardize the completion of the entire project.