AlterNet: Environment: Is This the Beginning of the End for Damming America’s Big Rivers?:

Currently there are 75,000 dams in the United States blocking 600,000 miles of river. In the West, over 100 salmon runs have gone extinct and 25 are listed as endangered.

That’s a lot of dammed water. Consider that are no natural lakes in some states (Georgia is reputed to be one) and ponder how much that alters the surrounding landscape.