Freshwater mussels excavated from three late Holocene sites on the West Fork and Clear Fork of the Trinity River in North Texas, are used to determine paleoenvironmental conditions, spatial turnover, and the effects of historic-period impoundments in these lotic systems.  The shell assemblages were analyzed based on species composition, abundance, habitat requirements of preserved species, and comparison with contemporary biogeographic distributions.  The faunal remains recovered suggest both streams near the archaeological sites were stable perennial free-flowing streams during the late Holocene. Species richness in both systems has been heavily impacted, with extirpations of prehistoric unionid species, followed by introduction of species into both the Clear Fork and West Fork of the Trinity River.