Abingdon, VirginiaTo an untrained eye, the crystal waters of the Clinch River, which meanders southwest across the Virginia-Tennessee border, look clean and healthy. But Jordan Richard can spot the dead bodies within seconds.

On a crisp fall morning on Sycamore Island, just before the Clinch crosses into Tennessee, Richard bends over to pluck a palm-size brown shell from the riverbed. What remains of the flesh that once clasped the two halves of the pheasantshell mussel (Actinonaias pectorosa) together now protrudes like a foul-smelling, gooey tongue. Noting that this mussel died within the past day or two, the U.S. Fish and Wildlife Service biologist tosses the shell into a labeled garbage bag for later analysis.

If he’s lucky, this deceased mollusk might