Threadfin shad impingement at 13 Tennessee Valley Authority electric generating plants from August 1974 through July 1975 was analyzed to assess mortality resulting from low water temperature. Concurrent laboratory experiments were conducted to evaluate the ability of cold-stressed threadfin shad to avoid impingement. Temperatures of 12°C stressed fish in the laboratory, while those below HOC caused high impingement mortality. At 5 of12 fossil-fuel plants, 90 percent or more orthe annual threadfin impingement occurred when water temperatures were below lOoC. At four plants, impingement was not related to low temperatures. Impingement at the Browns Ferry Nuclear Plant generally coincided with low water temperatures, but individual impingement peaks were not consistently associated with cold shocks.