Pre-impoundment bottom-fauna data are presented for the Watts Bar Reservoir area (Tennessee). A salting-out technique is described which was used to facilitate the separation of organisms from debris. In deep water four major taxonomic groups made up 98.93 per cent of the total number and practically 100 per cent of the total volume. Nymphs of Hexagenia bilineata (Say) composed 82.43 per cent of the total volume. This species probably has a 1-year life cycle in Tennessee. Production was highest on the muddy bottom and lowest on sand. Data on depth distribution showed the first 10 feet to be most productive. The seasonal peak of production was reached during September and October. This maximum was due almost entirely to mayflies. The rate of growth of Hexagenia nymphs was most rapid during August and September or immediately following hatching. The riffles and flats at the shallow-water station were less productive than the mud-sand bottom of the deep water. The fauna of the riffles and flats will probably not survive impoundment; however, the fauna of the deep-water area will survive.