Hydropower or hydroelectricity is the conversion of energy from moving water into electricity.

Water power is a renewable energy source because water movements are likely to last forever. Contemporary hydro plants produce electricity using turbines and generators. The mechanical energy created by moving water spins rotors on a turbine. The turbine is connected to a generator which produces electricity when the turbine spins.

There are two main types of hydroelectric power plants: dams and plants using the run of the river. A dam is a large barrier built to raise the level of water and control its flow. The high level of water created by the dam creates gravitational force for turning the turbine. Plants utilising the run of the river also have turbines and generators, but use the natural water flow of rivers. A portion of the river water goes into a long tunnel with turbines. These power plants depend on the amounts of water in rivers and are not as reliable as dams. When the level of water drops, they cannot produce electrical current.

Hydropower has several advantages. It is a cheaper source of electricity than sun and wind, even though the initial building cost can be high. It is quite reliable compared to other renewable options, because the flow of water in dams rarely stops. In some cases, dams can also help with flood control and be a water supply for communities living nearby. Critics say that river dams have a negative impact on the local environment by changing wildlife habitats, blocking movements of fish or forcing people in riverside communities to move out of their homes. Also, technical problems in dams can lead to serious catastrophes and threaten the lives of residents. Water power plants are also not completely free of carbon footprint because many lorries are used to transport cement for the construction of dams. They produce harmful gases and fumes, but compared to other renewable energy sources, water power is still one of the cleanest and eco‑friendliest ones.