text:  This is Morning Edition from NPR News. I'm Ian Martinez. And I'm Sasha Pfeiffer. Thousands of derelict dams used to power Appalachian mill towns. Now they're coming down. Their demolition restores the flow of rivers and streams. But that can threaten aquatic life, including America's largest amphibian. Zachary Turner with member station WFAE joined a recent search for the eastern hellbender.