Scott M. Smith, Virginia Department of Game and Inland Fisheries, 910 Thomas Jefferson Road, Forest, VA 24551

Many relationships have been derived from stream discharge and habitat, but few studies have examined relationships among stream discharge, habitat, and fish populations. I examined a coldwater stream fish assemblage before (1992-93) and after (1995-present) flow augmentation. Minimum flows in the Dan River, Virginia were changed from approximately 1.5 cfs to 8.9 cfs in 1994 (mean annual flow without project impacts = 73 cfs). In general, this stream became deeper and wider following flow augmentation although the degree of change varied among mesohabitats (pools, runs, riffles). Width and depth measurements were not significantly different (=0.10) between flow levels with the exception of runs, which became significantly deeper (mean depth and maximum depth). While the data is incomplete, brown trout Salmo trutta densities appear to have increased while densities of other species have shown no trends. Brown trout numbers were significantly greater in all mesohabitats following increases in flows, while brown trout biomass significantly increased in riffles and runs. The brown trout population may have expanded due to an increase in available habitat associated with the flow augmentation.