releasing water very sparingly, the TVA dams had created a "eutrophication" problem: In still waters, micro-organisms absorb oxygen needed fish, which either die or move away. The Bonneville Power Administration will spend up to $30 million to fit screens on its 15dams to keep migrating salmon from getting hacked up by the blades of the 60-foot turbines.
Most U.S. dams were designed and built long before the 1970 National Environmental Policy Act, which requires an ecological "impact"...