Physico-chemical factors, plankton, benthic macroinvertebrates, and fishes occurring in cold tailwaters below Beaver, Bull Shoals, and Norfork dams in northern Arkansas, were sampled regularly from July, 1965, through December, 1966. Physico-chemical conditions were similar in the three tailwaters throughout the study. The older tailwaters below Bull Shoals and Norfork dams were more productive than the Beaver tailwater in both phytoplankton and zooplankton. The greatest number of genera of plankton occurred in the Beaver tailwater, and the Bull Shoals tailwater had the least number. The majority of the benthic macroinvertebrates was comprised of only a few taxa. Samples from the Norfork tailwater contained more organisms and a higher average wet weight per square foot than did samples from the other two localities. Tendipedidae and Oligochaeta made up 91.0% of the total number of benthic macroinvertebrates in the Beaver tailwater; Tendipedidae and Amphipoda comprised 70.1% in the Bull Shoals tailwater. Isopoda and Tendipedidae accounted for 87.9% in the Norfork tailwater. Lists of fishes for the three tailwaters include 38 species. Five of these (Campostoma anomalum, Notropis galacturus, Notropis pilsbryi, Etheostoma caeruleum, and Cottus carolinae) were common to all three tailwaters. Cyprinids and sculpins were abundant below Bull Shoals and Norfork dams. The ichthyofauna below Beaver Dam exhibited a scarcity of cyprinids, with the exception of Campostoma anomalum, and an abundance of darters. Sculpins were rare below Beaver Dam.
