Despite the ecological importance and globally threatened status of freshwater bivalves, the freshwater mussel fauna of Turkey has hitherto received little attention. The aim of this study was to describe the ecology of freshwater mussels of the Lake Sapanca Basin (NW Turkey) to provide baseline data against which to measure future trends. Five native mussel species belonging to three genera were encountered in surveys; Anodonta cygnea, A. anatina, Unio pictorum, U. crassus and Dreissena polymorpha. In addition, an invasive species from Asia, A. woodiana, was recorded in the region for the first time. A. cygnea and U. pictorum were the most abundant species in the lake, while U. crassus was most abundant in the associated stream. Age and growth parameters were estimated for U. pictorum and U. crassus, and indicated that the latter species had a younger median age and faster growth rate than the former, possibly a function of exclusively occupying a nutrient enriched stream. The bio-ecological features of the bivalve fauna of the Lake Sapanca Basin, as well as the implications of the introduction of A. woodiana, are discussed.