Hydropower is electricity produced by moving water, and is used so widely in the U.S. that it generates more electricity than any other renewable source. Rushing water from a river or waterfall is channeled through pipes, spinning a turbine to drive a generator. Because the flow of water is relatively constant, except in times of drought, hydropower can deliver large amounts of continuous electricity over long periods of time.
Hydropower requires strong currents to produce significant amounts of electricity. Much of the hydropower in the United States is generated in the Pacific Northwest. Although hydropower is a renewable and inexhaustible electricity source, it does carry some associated environmental concerns. Building large dams can negatively impact local ecosystems and interfere with fish migration patterns. Technologies such as fish ladders can help reduce the environmental impacts of hydropower, but additional installations in the United States are unlikely to be large.
Other forms of hydropower can be used to produce electricity from moving water. Tide power and wave power provide new ways to create electricity from the oceans. Tidal barrages have been in existence for decades, but they are often expensive and pose similar environmental concerns to dams. Newer methods may produce cheaper electricity with less environmental impact. The Aguçadoura Wave Farm in Portugal, built by Pelamis, is the world's first utility-scale wave farm. It features snakelike turbines with a series of hydraulic rams. A second installation is planned off the coast of Scotland.