Hydroelectric energy converts the kinetic energy of flowing water into electricity using a turbine. Water flows through a channel, usually carefully regulated as part of a dam spillway, and it turns the blades of the turbine. As long as water continues to flow steadily, the turbine produces a steady stream of electricity. The U.S. Geological Survey Science School states that 19 percent of the world's electricity comes from hydroelectric energy.
Hydroelectric power offers the ability to create electricity without carbon emissions, and it is more reliable than wind or solar power. However, hydroelectric plants usually rely on dams to provide a steady stream of water, and that construction can have an environmental impact of its own. A hydroelectric plant can disrupt the natural migration of fish and other animals that depend on the waterway, and the dam often creates a large reservoir that can displace animals and people.
Hydroelectric dams can be enormous structures, and their construction can completely alter the hydrologic face of an entire region. Also, when a dam fails, it can present a major threat to those living downstream. Since a hydroelectric plant traps a large volume of water and allows it to pass through at a reduced rate, a sudden release of stored water can create dangerous floods.