The primary source of energy for hydroelectric power is the movement of water, specifically from rivers and reservoirs. Hydroelectric power plants generate electricity by harnessing the kinetic energy of flowing water, typically through the use of dams. As water flows through turbines, it converts mechanical energy into electrical energy, providing a renewable and sustainable power source. This form of energy production reduces greenhouse gas emissions and dependence on fossil fuels, making it an essential component of modern energy strategies.