Hydroelectric energy—electric power created by the kinetic energy of moving water—plays an important role in supplying the world's electricity. In 1996, nearly 13 trillion kilowatt-hours of electricity were generated worldwide; almost one-fifth of this electricity was produced with hydroelectricity. On average hydropower provides about ten percent of the U.S. electricity supply, although the annual amount of electricity generated by hydroelectric resources varies due to fluctuations in precipitation. In many parts of the world, reliance on hydropower is much higher than in the United States. This is particularly true for countries in South America where abundant hydroelectric resources exist. In Brazil, for example, 92 percent of the 287 billion kilowatt-hours of electricity generated in 1996 were generated by hydroelectricity.

There are many benefits for using hydro resources to produce electricity. First, hydropower is a renewable resource; oil, natural gas, and coal reserves may be depleted over time. Second, hydro...