Lake Powell is a reservoir on the Colorado River, straddling the border between Utah and Arizona (most of it, along with Rainbow Bridge, is in Utah). It is the second largest man-made reservoir in maximum water capacity in the United States behind Lake Mead, storing 24,322,000 acre feet (3.0001×1010 m3) of water when full. Current water levels, however, put Lake Powell ahead of Lake Mead in water volume and surface area. Lake Powell was created by the flooding of Glen Canyon by the controversial Glen Canyon Dam, which also led to the creation of Glen Canyon National Recreation Area, a popular summer destination. The reservoir is named for explorer John Wesley Powell, a one-armed American Civil War veteran who explored the river via three wooden boats in 1869. In 1972, Glen Canyon National Recreation Area was established. It is public land managed by the National Park Service, and available to the public for recreational purposes. It lies in parts of Garfield, Kane, and San Juan counties in southern Utah, and Coconino County in northern Arizona. The northern limits of the lake extend at least as far as the Hite Crossing Bridge. A map centered at the confluence of the Escalante River 37°17′22″N 110°52′20″W with the Colorado River gives a good view of the extent of the lake.

Lake Powell is a storage facility for the Upper Basin states of the Colorado River Compact (Colorado, Utah, Wyoming, and New Mexico). The Compact specifies that the Upper Basin states are to provide a minimum annual flow of 7,500,000 acre feet (9.3 km3) to the Lower Basin states (Arizona, Nevada, and California).