Freshwater mussels are disappearing—and no one is really sure why

April 14, 2026

17 min read

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Freshwater mussels are disappearing—and no one is really sure why

Biologists are racing to save America’s freshwater mussels—the water-filtering keystone species that once filled the country’s rivers and streams—from extinction

By Robert Kunzig edited by Seth Fletcher

American streambeds were once paved with these beautiful burrowing creatures—300 species of them. Some 10 percent are extinct already. Many more are endangered, including the Northern riffleshell (pale with fine green rays, at bottom) and the clubshell (with darker splotches, at middle).

Ryan Hagerty/U.S. Fish and Wildlife Service

Through my swim mask, I could see what Wendell Haag’s finger was pointing at two feet below me on the riverbed. But I couldn’t immediately see that it was alive. It looked like a rock with some kind of grayish goo stuck to it. We were in the South Fork of the Kentucky River, and I was on my hands and knees with my face in the water and my backside in the air—an inelegant pose I had learned from mussel biologists such as Haag. Finally, after a long, dumb stare, I recognized the mussel. It was mostly buried, but it, too, had left its posterior exposed, and the shell was slightly agape. Draped around that dark slit were fleshy protrusions that flapped like pennants in the current. The mussel, called a pocketbook, was fishing for bass.

A bass, it seems, would mistake those protrusions for an edible minnow. It would snap at the lure, whereupon, instead of food, it would get a mouth blast of mussel larvae—thousands of bivalved vampires smaller than salt grains, some of which would immediately latch on to its gills and start feeding on its blood.

When I first learned about this scenario, it caused me to think differently, and with more respect, about the pocketbook. And not just the pocketbook: roughly 300 species of freshwater mussel have been documented in North America. All of them are brainless invertebrates. They spend most of their lives lodged in riverbeds, filtering algae and bacteria from the passing water. Yet they all get fish to spread their spawn, and most deploy elaborate stratagems. Some mussels, like the pocketbook, convince a fish to bite into a lure full of larvae; others first snap their shell shut around the fish’s head and spray their babies into its mouth. The larvae spend several weeks attached to the fish’s gills, metamorphosing into juvenile mussels, then let go and drop to the riverbed. Often—and this is the point of the whole scheme—it will be upstream from where they boarded the fish.

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Freshwater mussels evolved from marine bivalves more than 200 million years ago, colonizing rivers by getting fish to carry their larvae upstream. Marine mussels are the kind many people like to eat. Freshwater mussels are the kind most people don’t even know exist. They live for decades—more than a century in some cases.

But these days the freshwater species are vanishing. Around a tenth of the 300 in North America have gone extinct already, and a third of the survivors are listed as endangered or threatened. That’s more puzzling than it might sound. Even though we’ve stopped building dams that destroy mussel habitat, even though we pollute rivers much less than we used to, most mussel populations have continued to decline. Scientists aren’t sure why. “There’s this environmental catastrophe going on, and we really don’t know what’s causing it,” Haag said.

Haag belongs to a small community of researchers who are trying to stop it. In a half dozen state-run laboratories around the Southeast, the world hotspot of mussel diversity, researchers have perfected techniques for breeding rare mussels in captivity and then releasing them into rivers. For his part, Haag is leading a 13-state study of some 90 streams to look for the cause of the “enigmatic declines,” as he calls them. There is still reason to hope, he thinks, that the drop-off can be reversed.

Last summer I plunged into four different Kentucky rivers with Haag, a U.S. Forest Service stream ecologist in Frankfort. He took me first to a stream that had so far been spared a serious decline—the Rolling Fork, on the southern edge of the Bluegrass region—to show me the kind of mussel population that was still common back in the 1980s, when he chose his path in life. Sprawled in that shallow river, even I was able to find six different species in a square yard of riverbed. Haag found many more. “We’re walking on mussels here,” he said.

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