Hydropower comes in many forms, though most people still associate it with big dams. In the heyday of dam building, projects like Grand Coulee Dam and Boulder Dam in the American West were monumental efforts. But back then, we didn't fully understand how dams could disrupt ecosystems; now we do, and as a result, large dams have fallen out of favor in many places. And where the U.S. was once the leader in large scale hydropower, we're now removing more dams than we're building. Today, the biggest obstacles to constructing new hydroelectric projects in the U.S. aren't just environmental—they're economic and regulatory. But hydropower is a very site-specific technology—and there are plenty of ways to make it more environmentally friendly. Closing the Gap is hosted by Gwen Holdmann and edited by Jennifer Pemberton. This episode was produced by Tony Williams. Music is from Blue Dot Sessions.