A hydroelectric dam is a structure built across a river to harness the energy of flowing water. It works by blocking the river's flow, creating a reservoir or lake behind the dam. When water is released, it flows through turbines, which convert the water's kinetic energy into mechanical energy, and then into electrical energy. These dams are a significant source of renewable energy, providing electricity to homes and businesses. They also help with flood control and irrigation. However, building a hydroelectric dam can impact local ecosystems and communities, as it alters natural water flow and habitats.