Hydroelectricity is electricity that is made by the movement of water. It is usually made with dams that block a river to make a reservoir or collect water that is pumped there. When the water is "let go", the huge pressure behind the dam forces the water down pipes that lead to a turbine. This causes the turbine to turn, which turns a generator which makes electricity. This use of renewable energy produces less pollution than steam engines do. Some places such as Norway and Quebec get most of their electricity this way.