Lake Havasu is a large reservoir formed by Parker Dam on the Colorado River, on the border between San Bernardino County, California and Mohave County, Arizona. Lake Havasu City sits on the Arizonan side of the lake with its Californian counterpart of Havasu Lake directly across the lake. The reservoir has an available capacity of 619,400 acre-feet (0.7640 km3). The concrete arch dam was built by the United States Bureau of Reclamation between 1934 and 1938. The lake's primary purpose is to store water for pumping into two aqueducts. Prior to the dam construction, the area was home to the Mojave people. The lake was named after the Mojave word for blue. In the early 19th century, it was frequented by beaver trappers. Spaniards also began to mine the areas along the river.

Parker Dam is a concrete arch-gravity dam that crosses the Colorado River 155 miles (249 km) downstream of Hoover Dam. Built between 1934 and 1938 by the Bureau of Reclamation, it is 320 feet (98 m) high, 235 feet (72 m) of which are below the riverbed (the deep excavation was necessary in order to reach the bedrock on which the foundation of the dam was built), making it the deepest dam in the world. The portion of the dam above the foundation stands 85 feet (25.9 m) tall, making it the only dam in the world that stands more underground than above ground. The dam's primary functions are to create a reservoir, and to generate hydroelectric power. The reservoir behind the dam is called Lake Havasu and can store 647,000 acre⋅ft (798,000,000 m3; 2.11×1011 US gal; 1.76×1011 imp gal). The dam straddles the Arizona-California state border at the narrows the river passes through between the Whipple Mountains in San Bernardino County, California and the Buckskin Mountains in La Paz County, Arizona.