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2 -regular,_-containing, _5%..rotenone-, were applied to the Grego -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 R above the present site of -Flaming..-Gorge Dam, a distance-o-f -approximately 225 miles. To prevent destruction of fish and aquatic invertebrates in Dino- _ aaur. National- Monument:, .5D., 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- =I. aaaium .permanganate wera::diiq),ensed- from -this station- to:..detnzLi=the --: __4' -fy,7 rotenone. Personpel.monitoring the river during the project felt that the detoxification was largely successful (Binns et al., 1963). Park -- :--..angers patrn_11ing the river,. aim-Ithe- Monument during--and: s tay aver: the fish control project; however, saw many dead and distressed fish. Whether these sightings indicated a passage of rotenone into the Monu- ment or, :the,dri:ftiug,;o€ di-sabled,-fah into the- Monument i'ron-ab v& was not known. In either case it seems certain that the rotenone application re- -su ted'in a nearly complete killof 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 --foll-owing the-roterione -appH--a-ti-on. -- 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, - -wa•s 91-ov to?-re--€?s-tab-fish i-t-s-ei`f--throughout the river 'above the dam .. 0 (Binns, 1965).