The water flowing in a river is collected b constructing  a big dam where the water is stored and allowed to fall from a height. The blades of the turbine located at the bottom of dam move with the fast moving water which in turn rotate the generator and produces electricity. We can also construct mini or micro hydel power plants on the rivers in hilly regions for harvesting the hydro energy on a small scale.

But the minimum height of the water falls should be ten metres.the hydro power potential of India is estimated to be about 4*10 to power of 11 killowatt hours. Till now we have utilized only a little more than 11 percent of this potential.hydropower does not cause any pollution. It is renewable and normally the hydropower projects are multi-purpose projects helping controlling floods, used for irrigation,navigation etc. however, big dams are often associated with a number of environmental impacts which have already been discussed in the previous section.