The species originally occurred throughout the medium-sized and large rivers of the Colorado River Basin, but its range has shrunk to the river above the Grand Canyon, and to Lake Mead, Lake Mohave, and Lake Havasu on the lower part of the river. The reason for the decline is largely due to habitat loss. The state of California designated it as endangered in 1974, followed by the United States government in 1991. A population of over 3,000 fish in Lake Mohave has been created by an augmentation program using fry that were produced naturally in the lake. In addition, reintroduction programs have released hatchery-raised fish into Lake Havasu, the Colorado River below Parker Dam, and the Verde River.