The banks of the Potomac River upstream from Washington, D.C., are often mounded with drifts of tiny shells bleached white by the sun. That invertebrate abundance startles me every time I walk the riverbank, a clue to an invisible city of bivalves under the water. In this issue, freelance writer Stephen Ornes takes us to Appalachia, where he chronicles scientists’ dogged work to restore an endangered species of mussel, the golden riffleshell . Freshwater mussels used to be incredibly common in the United States, but dams and pollution have taken a toll. It’s a clear loss, because the humble creatures play an outsize role in riparian ecosystems, and in public health: More than two-thirds of U.S. homes get their drinking water from rivers, and mussels excel at cleaning water. Ornes, who lives in Nashville, was looking forward to wading streams with the researchers doing the work, but the pandemic scotched those plans. Instead, multiple phone interviews helped him re-create the painstak