Another way people obtain energy is through the use of flowing water. Hydroelectric energy is one of the oldest sources of energy. Hydroelectric energy is generated when water spins a turbine. Thousands of years ago, water was used to turn a paddle wheel to grind grain, like a windmill. Actual hydroelectric power plants that produce electrical energy have been in use in the United States since 1882.

Hydroelectric Systems
There are two main types of hydroelectric systems. In a “run-of-the-river system,” the force of the water’s current provides the energy to power the turbine. In a “storage system,” water is collected in reservoirs created by dams, then released when needed. Hoover Dam in the United States and the Three Gorges Dam on the Yangtze River in China are examples of hydroelectric storage systems. When Hoover Dam was constructed, Lake Mead was formed as a result, and became the storage reservoir for the hydroelectric power plant.

Advantages and Limitations
Many feel that hydroelectric energy holds great promise as an energy source for our future. Unlike fossil fuels or nuclear energy, hydroelectric power is renewable; water is recycled on the planet through the water cycle.

On the other hand, some believe that hydroelectric power plants are disruptive to the ecosystem. In the Columbia River, for instance, a series of dams get in the way of salmon trying to swim upstream to spawn. Different solutions are being offered to remedy the situation. For example, engineers have added “fish ladders” to the system which help the salmon “step up” the dam to the spawning grounds upstream. However, hydroelectric energy continues to have its critics. Disruptions caused to the land can cause negative effects for both human and animal life.