Hydroelectric schemes are systems that generate electricity by using the energy of flowing or falling water. Typically, a dam is built on a river to create a reservoir, which stores water. When water is released from the reservoir, it flows through turbines, causing them to spin and generate electricity. This process is a renewable energy source, as it relies on the natural water cycle. These schemes can vary in size, from large-scale projects like the Three Gorges Dam in China to smaller community-based systems. Hydroelectric power is considered environmentally friendly, as it produces no direct emissions and helps reduce reliance on fossil fuels.