Hydroelectricity is electricity made by generators that are turned by the movement of water. It is usually made with dams that partly block a river to make a reservoir of water. Water is released, and the pressure of the dam (potential energy stored in the dam) forces the water down pipes that lead to a turbine. This causes the turbine to turn, to turn a generator which makes electricity.
This renewable energy method makes about one sixth of the world's electricity. It produces less pollution than the fires of steam engines do. Some places such as Norway and Quebec get most of their electricity this way.
Because all methods have advantages and disadvantages, most countries have several ways to generate electricity. For example, hydroelectric methods have certain advantages, and atomic energy has quite different advantage.For most countries today, hydroelectric energy is the preferred, or one of the preferred methods. Mainly because it is a renewable energy which means that you can reuse it and it will never run out.