The Susquehanna River Basin is the largest in Pennsylvania and contains globally significant populations of yellow lampmussel (Lampsilis cariosa), as well as supporting other freshwater mussel species of concern. Basinwide surveys have not been conducted since the mid 1990’s and almost no information is available on density and abundance. This project focused on the Lower Susquehanna River Sub-basin as the final sub-basin to be surveyed in a series of projects. We surveyed a total of 32 sites using a two phase sampling design (Smith et al. 2001) combining timed searches and quantitative, quadrat based surveys. We found a total of 9 species throughout the sub-basin. The highest species richness was found at sites on the Susquehanna River mainstem and at a site on Penns Creek, with 7-8 species per site.