Final answer:
The Hoover Dam creates the largest reservoir in the United States, Lake Mead, as well as a significant hydroelectric power plant and a recreational area. It was once the world's largest such power plant and the tallest dam at the time of its construction.
Step-by-step explanation:
The Hoover Dam backs up the Colorado River and creates several features. Primarily, it creates a reservoir known as Lake Mead, which is the largest reservoir in the United States in terms of water capacity. The dam also houses a hydroelectric power plant which was the largest of its kind from 1939 to 1949. This facility was constructed between 1931 and 1935 and was, at the time, the tallest dam and largest concrete structure in the world.
Besides, the dam and the reservoir also create a recreational area for activities such as fishing, boating, and sightseeing. Although not explicitly mentioned in the creation of the Hoover Dam, a canal system as part of the broader network of the Colorado River allows for agricultural irrigation and water supply delivery, particularly in the American Southwest.