The most common type of hydroelectric power plant is an impoundment facility. An
impoundment facility, typically a large hydropower system, uses a dam to store
river water in a reservoir. Water released from the reservoir flows through a
turbine, spinning it, which in turn activates a generator to produce
electricity. The water may be released to meet changing electricity needs or
other needs, such as flood control, recreation, fish passage, and other
environmental and water quality needs.