Boulder Dam was the original name of what is now known as Hoover Dam, renamed in honor of Herbert Hoover. The dam is 726 feet (221 m) above the Colorado River bed between Nevada and Arizona and was the world's largest dam at the time of its completion. Many significant innovations were incorporated into its construction. It is a gravity arch dam used for flood control, hydroelectric power, and water for drinking and irrigation. It serves areas as far away as southern California. Behind the dam is the 115-mile-long (185 m) reservoir Lake Mead, which is a popular recreation area.