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was determined with the use of a carbon analyzer. Particulates were sized into fractions (0.45-10 pm, 10-165 pm. and 355-1000 pm) by passing known volumes of water sequentially through the different mesh sizes. Particulate organic carbon from 355 pm to 1 cm was collected using insect drift nets. Nets were set in place for a timed interval at minimum discharqe from Libby Dam and flow rate monitored to quantify the volume filtered. All insects and debris larger than 1 cm was removed prior to analysis for ash-free dry weight. Periphyton species identifications were made by Dr. Lor~n Bahls of Montana Department of Environmental Sciences who analY7~d periphyton community structure using methods described in Bahls, et al. (1979). The substrate was characterized at each of the four sampling stations. The intermediate axis (the widest width) was measured on all surface rocks in an 0.33 m2 area. Six replicate samples were taken at random from the zone flooded with flows of 20,000 cfs down to 4,000 cfs. Sampling was done at minimum discharge from Libby Dam. Replicate samples taken from subsurface rocks were fractionated into six size classes (>50, 50- 19, 19-16, 16-2, 2-.063 and <.063 mm) using soil sieving techniques. A heterogeneity index (Schwoerbel 1961) was calculated for the subsurface samples. Heterogeneity (degree of particle size diversity) was calculated by making a plot of the cumulative percentage by weight against the particle size (mm); heterogeneity = particle size 60%/particle size 10%. In order to determine the benthic community associations which have resulted from regulation of the Kootenai River, the biological data was reduced to fewer variables with the use of diversity indices and three ' ordination techniques. These methods were applied to data obtained from collections which were made in October, 1979 and January, March and July, 1980. number of taxa in s = zNi. A value i of zero is obtained when all individuals belong to the same species. The maximum value of H' depends on the number of individuals counted and is obtained when all individuals belong to different species. H' usually varies between three and four in natural stream areas and is usually less than one in polluted or stressed stream areas. The Shannon diversity index was calculated after samples were pooled by sampler type at each sample station and date. The formula used for s N' N' the Shannon function was H' = ETNt 1092TNt where s i sample, Ni = number of individuals in taxon i, and N Evenness (Ev)' as measured by Margalef (1957), is a ratio of the observed HI to a maximum theoretical diversity (H'max)' computed with all individuals equally distributed among the species. Maximum diversity (H'max) was computed as 1092s; therefore evenness = H' Evenness 1092s generally ranges between 0 and 1. Perturbation reduces Ev below 0.5 and generally to a range of 0.0 to 0.3. -6-