Until Glen Canyon Dam was completed in 1963, the Colorado River's aquatic system was dominated by native fish. These native species were specifically adapted to highly variable seasonal fluctuations in sediment load, flow, and temperature, and were severely impacted by dramatic changes resulting from the dam. The introduction of non-native fish contributed to competition and direct mortality. Predation on native fish has been documented for channel catfish, black bullhead, brown trout, and rainbow trout, and competition is implied for many species. Of the eight native species found in the River before 1963, three species are now extirpated (the Colorado squawfish, bonytail chub and roundtail chub), two species are federally listed as endangered (the humpback chub and razorback sucker*), and three species (the speckled dace, flannelmouth sucker, and bluehead sucker) still have adequate populations.
Programs to introduce non-native species for sport and food began at the turn of the century. Most releases were cool-water fish, although warm-water fish, including carp and brown trout from the Eastern U.S., were also stocked. Trout were introduced for sport purposes by the National Park Service (NPS), Arizona Game and Fish Department (AGFD), and the US Fish and Wildlife Service (USFWS) in the 1920s. While the NPS ceased stocking in 1964, AGFD continued to plant rainbow trout near Lees Ferry until the 1990's. Twenty-four species of non-native fishes have been reported in Grand Canyon since 1958 with approximately 12 present today. This number may increase in the future, as fish stocked in Lake Mead continue to move upriver into the park.
A current state fishing license is required to catch fish in the Park. Special artificial lure regulations and bag limits apply to various stretches of the Colorado River.