Powered by the sun, the hydrologic cycle re-charges rivers and is essentially infinite. Hydropower converts falling water into electricity without using more water than is produced by nature. Of the 75,187 existing dams in the U.S., less than 3 percent are used to generate electricity. There is an additional 21,000 megawatts of hydroelectric capacity at sites with an already existing dam. In all, there is nearly 30,000 megawatts of potential hydropower capacity at 5,677 sites that have been screened by the Department of Energy for environmental, legal and institutional constraints.
Dams can enhance wetlands and support healthy fisheries.
Wildlife preserves can be created around reservoirs which, in some cases, provide stable habitats for endangered or threatened species. There were a total of 81 million recreation user days provided at FERC licensed hydropower projects in 1990. Boating, skiing, camping, picnic areas and boat launch facilities are all supported by hydropower. And Inexpensive Today's hydropower turbines are capable of converting 90 percent of available energy into electricity. That is more efficient than any other form of generation.