The unionid mussel fauna of Kentucky Lake has changed significantly over the past century. Prior to the completion of Kentucky Dam in 1944, 42 species had been reported from the mainstem Tennessee River now inundated by Kentucky Lake. After Kentucky Dam was completed, the tailwater fauna experienced minor change in species richness with 38 species being reported between 1978 and 1985. Currently, the Kentucky portion of Kentucky Lake supports 21 species. Four of these were not reported in the historical fauna prior to impoundment: Anodonta suborbiculata, Plectomerus dombeyanus, Potamilus ohiensis, and Toxolasma parvus; thus only 17 of the original species survived impoundment while four species invaded after Kentucky Dam was constructed. Amblema plicata is now the most abundant species. Plectomerus dombeyanus, first found in the Tennessee River in 1981, is the second most abundant mussel in the Kentucky portion of Kentucky Lake. Quadrula quadrula peaked in relative abundance at 51% in 1989 but subsequently declined to 10% by 2001. Few mussels survive in the deep channel where fine sediment continues to accumulate and anaerobic conditions sometimes occur. The faunal decline is typical following large dam construction, while the continuing change in the mussel fauna may reflect an aging reservoir and invasion of opportunistic species.