Some freshwater mussels are the size of a button. Others are as big as a deck of cards. They have charming names like fluted kidneyshell, snuffbox, and shiny pigtoe. Their job is to clean up river water. But mussels in one river are dying. Scientists search for clues to help save them.

The mystery unfolds in the Clinch River in Kyles Ford, Tennessee. More mussels live there than people. The Clinch River winds 300 miles through Appalachia. Forty-six species of mussels make their homes in the river. Each of those species is a family with hundreds of thousands of members.

Jordan Richard is a biologist for the U.S. Fish and Wildlife Service. His job keeps him slogging through water in search of mussels. He’s got a good eye for them. That’s a good thing since mussels are great at hide-and-seek. Mussels bury themselves in the riverbed. They leave only a crescent of their shells visible.

But now the white shells of dead mussels litter the river bottom. Hundreds of thousands, possibly millions, of pheasantshell mussels have died in the water. No one knows why. Scientists know that pollution, habitat loss, and disease can wipe mussels out. But they haven’t figured out what healthy mussels look like inside. What makes them grow? What keeps them strong?  

Tony Goldberg is an epidemiologist. He studies diseases. His latest “patients” are freshwater mussels. He knows rivers need mussels. They may not have a backbone, but they are hard workers. They filter water for fish, amphibians, insects, and even people.

Wisconsin, Michigan, the Pacific Northwest, and Spain have also launched investigations into disappearing mussels. Oddly enough, their mussels don’t appear to be dying from the same problem. In a way, that’s good news. It means one terrible disease isn’t going to wipe out all mussels. But it doesn’t solve the mystery.

Here is the sea, great and wide, which teems with creatures innumerable, living things both small and great. — Psalm 104:25