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.