On "good" bad days, the shells lie open at the bottom of the river, shimmering in the refracted sunlight. Their insides, pearl white and picked clean of flesh, flicker against the dark riverbed like a beacon, alerting the world above to a problem below. "That's what we look for in die-offs," says biologist Jordan Richard, standing knee-deep in the slow-flowing waters of the Clinch River in southwest Virginia. He points at a faint shape submerged about 10 feet upstream. "I can tell from here that's a pheasantshell, it's dead and it died recently. The algae development is really light." The pheasantshell is a freshwater mussel, a less-edible version of its saltwater cousin that spends most of its inconspicuous life part-buried in riverbeds, blending in with the rocks and filtering the water around them. In recent years, though, biologists and fishermen noticed something was wrong. On sections of the Clinch and other waterways in the Pacific Northwest and Midwest, dead mussels were
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