Hoover Dam, with its elegantly arching shape and smooth, towering walls represents an idea even bigger than itself. The dam symbolizes human ingenuity and our ability to transform the environment and make even a harsh desert habitable. By generating power, controlling downstream flooding, and storing water for irrigation and municipal use, Hoover Dam fueled the growth of the American Southwest.

Lake Mead, the reservoir Hoover Dam creates by holding back the Colorado River, holds 35 billion cubic meters (46 billion cubic yards) of water, which generates tremendous force. The water pressure near the base of the dam is close to 220,000 kilograms per square meter (45,000 pounds per square foot). The dam resists this force -- otherwise it wouldn't remain standing. It also harnesses this force and uses it to generate electricity.

Hoover Dam doesn't stand as an impenetrable barrier to the water in the reservoir. It constantly releases water at a rate of about 15,000 cubic meters (20,000 cubic yards) each second, which is more than half the water in an Olympic-sized swimming pool. Inside the dam are 17 hydroelectric generators, each attached to a huge fan-like structure called a turbine. As water is released from the reservoir, it flows through pipes in the dam and past the turbine blades, causing the turbines to spin and the generators to which they're attached to turn.

Generators, including those in Hoover Dam, produce electricity through a process called electromagnetic induction. When a loop of wire moves through a magnetic field, or vice versa, an electrical current is produced. As the turbines in Hoover Dam spin, they cause electromagnets to turn inside stationary wire loops, inducing current in those loops.

Hoover Dam generates more than 4 billion kilowatt-hours of electricity each year, enough to serve 1.3 million people. Still, this efficient and seemingly cheap source of power is not without its costs. Dams create impenetrable barriers to spawning fish, and large reservoirs destroy important and uncommon river and canyon wildlife habitat. They can also disrupt human habitat and submerge land that has been traditionally available for other uses. For these reasons, environmental groups decry the existence of dams like Hoover Dam and oppose the construction of additional ones.