Electricity is produced by a device called a turbine. Turbines contain metal coils surrounded by magnets. When the magnets spin over the metal coils, electricity is produced. Turbines are located inside dams. The falling water spins the magnets.
Dams provide clean, pollution free energy, but they can also harm the environment.
Species that use rivers to spawn are often hurt by dams. In the Northwest, sockeye salmon and trout populations have dropped from 16 million to 2.5 million since hydroelectric plants were built on the Columbia River. Dams all over the world have hurt some species. The highest dam in the Unites States is located near Oroville, California. The Hoover Dam, on the Nevada-Arizona border controls the Colorado river.