Levels of environmental protection vary among watersheds, and assessing how well conservation efforts protect threatened faunal groups is a critical need for management. Almost the entire 114 km of the Chagrin River is designated as scenic by the state of Ohio, which implies good water quality and community efforts to maintain and improve water resource integrity. We examined mussel diversity and abundance across 30 sites. The mussels present remained largely restricted to the upper reaches. One species, Lampsilis radiata luteola, dominated the assemblage of the upper Chagrin, which now includes only six additional species, none of which are very abundant: Lasmigona costata, Lasmigona compressa, Pyganodon grandis, Strophitus undulatus, Utterbackia imbecillis, and Anodontoides ferussacianus. One additional species, Lampsilis cardium, was the only species found living in the lower Chagrin. Applying the Shannon index of diversity indicated that the Chagrin River has a more depauperate fauna than neighboring watersheds, and therefore, the current passive conservation efforts may be insufficient to protect these small isolated populations of remaining species.