HydroelecTricity?
power generated by water.
usually held back by a dam, water is released through impellers, turning turbines on generators, creating electric current.
When it is higher up, water has more energy (potential energy in this case). When it falls down, this is converted into kinetic energy (movement), which in turn is converted by a generator into electricity.
Usually, the hydro-projects are located in hilly areas with gradient differences so that potential energy of water at higher altitude can be utilised. These are the areas generally with forests and diversified flora and fauna. The river water has to be collected in a dam and that drowns a lot of forest and valley. Each valley is unique (read about 'the silent valley'). The back waters of the dam may run into kilometers!! If projects are not very large it is a good idea the energy is clean.