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The daily flow regime, which was relatively stable under natural conditions, now fluctuates due to the power peaking capability of Libby Dam. Daily flows can fluctuate a maximum of four vertical feet per day from April through September and six feet per day from October through March. Actual fluctuations have been less than the maximum criteria on most days. From April, 1972 through June, 1975, water was released from either the dam sluices, the spillways or a combination of the two. The water fall ing into a 60-foot deep still ing basin resul ted in gas s'lpersaturation levels averaging 135 percent. Supersaturation persisted at somewhat lower 1 evel s downstream to Kootena i Falls, a di stance of 29 mil es. Beginn ing in July, 1975, increasing amounts of water began to be discharged via the penstocks as installation of the first four generators was completed. By the end of March, 1976, penstock discharges had reduced gas saturation levels to near 100 percent. Sluice and spillway discharges and associated gas supersaturation have been infrequent since this date. The water temperature regime in the Kootenai River has been significantly altered by regulation. Sluiceway and spillway operation from 1972 through 1976 resulted in unusual tempera ture patterns. Di scharge temperatures during the summer varied from about 8.20C (470F) to 18.30C (650F). These patterns were modified when the selective withdrawal system became operational in June, 1977. A temperature rule curve was developed for operating the system. Winter discharges are from deep within the reservoir and temperatures are generally near 4.0oC (390F). As the reservoir fills, the selective withdrawal is operated to withdraw water no closer than 50 feet from pool surface (to reduce escapement of fish from the reservoir) and maintain a maximum temperature of 13.50C (560F). The operation of the system provides temperatures which are warmer than the natural regime from October to March, and cooler from April through September. Flow regulation el iminated. the spring flood flows which had maintained the river channel morphometry and resorted substrate materials. Decreased peak flows also allowed deltas to build around tributary stream mouths. The reservoir acts as a sediment and nutrient trap and reduces the concentrations of these water quality constituents in downstream water. Impoundment of the river has decreased available allochthonius materials, but sestonic drift from the reservoir area has increased. A survey of the aquatic insects in the Kootenai River in Montana was done as part of the Corps of Engineers preimpoundment water quality study from 1967-1972 (Bonde and Bush 1975). Limited macroinvertebrate sampling done near Kootenai Falls 47 km (29 miles) downstream from Libby Dam (Graham 1979) indicated major changes in insect diversity and composition since impoundment. Little fish data were collected on the Kootenai River prior to 1969 except for creel surveys conducted by game wardens. Testing of electro- fishing gear and development of sampling methodology began in 1969 and the first population estimates were obtained in 1971 in the Jennings Section, vi