Freshwater mussel beds of the lower 68 km of the Cache River, AR, were delineated and sampled using diving and stratified random sampling methodology to determine species richness, density, size structure, and population and community numerical standing crop (CNSC). A total of 38 mussel beds were delineated, including 14 major beds (Mbeds) and 24 minor beds (mbeds). Twenty six species were collected, four of which were previously unknown from the Cache River. Amblema plicata, Megalonaias nervosa, and Plectomerus dombeyanus were the most abundant. Estimates of CNSC ranged from 3705 ± 1908 to 122,115 ± 24,194 individuals in Mbeds with mean densities ranging from 6.2 to 44.1 mussels/m². Nine of 16 species with > 10 individuals had a unimodal size frequency distribution and the other seven had multi-modal distributions. This study found impressive mussel assemblages in the lower Cache River, previously thought to contain only refugial pockets of mussel assemblages. Further monitoring of some species is recommended based on lack of recruitment.