Dams are usually ecological disasters. The Hetch Hetchy Valley was dammed up and it destroyed a natural resource on par with Yosemite. People have been trying t

Dams are usually ecological disasters. The Hetch Hetchy Valley was dammed up and it destroyed a natural resource on par with Yosemite. People have been trying to remove it for years, but the San Francisco residents refuse to let it go since it supplies such a large amount of power to them.