Water constantly moves through an immense global cycle, evaporating from lakes and oceans all over the world, condensing to form clouds, precipitating as rain and snow, which then flows back to the oceans. Hydroelectric power takes advantage of this water cycle to drive machinery or create electricity. Hydroelectric power uses moving water as energy. Because the water cycle is an endless and constantly recharging system, it is an excellent source of renewable energy. Traditional hydroelectric power takes the energy of moving water to turn hydraulic turbine blades. The blades then turn a generator shaft that produces mechanical energy. The generator converts this energy into electricity. Engineers have developed innovative technologies that take advantage of other sources of energy from water including ocean currents, tides and waves.