Nonnative fish species were introduced to the Colorado River prior to the completion of the Glen Canyon Dam in 1963. Walleye (Stizostedion vitreum), bluegill (Lepomis macrochirus), green sunfish (L. cyanellus), European carp (Cyprinus carpio), and channel catfish (Ictalurus punctatus) are present in Lake Powell and developed from stock already present in the river system before the dam was completed.
Some nonnative fish were unable to survive the environmental changes caused by the filling of Lake Powell. These fish, which include the fathead minnow (Pimephales promelas), mosquitofish (Gambusia affinis), and plains killifish (Fundulus zebrinus), are still present in Glen Canyon NRA, but are now mainly found in the flowing rivers, inflows, and small perennial tributaries. Red shiner (Cyprinella lutrensis) established a marginal population in Lake Powell, but are more commonly found in flowing water.
Smallmouth bass (Morone dolomieu) and striped bass (M. saxatilis) were introduced to Lake Powell because of their preference for open habitat and now dominate the fish community. Other nonnative fish, such as largemouth bass (Micropterus salmoides) and black crappie (Poxomis nigromaculatus), were introduced to Lake Powell to provide outstanding recreational sport fishing opportunities. To provide additional forage for these sport fish species that live in the upper layers of open water, threadfin shad (Dorosoma petenense) were introduced in 1968. Rainbow trout (Oncorhynchus mykiss) were stocked in the water released from the dam in the Lees Ferry area.
Though native fish species were declining prior to the construction of Glen Canyon Dam, nonnative fish compete with and predate on native species. With proper management and planning, Glen Canyon NRA can preserve the remaining unique native fish and provide excellent recreational sport fishing opportunities of nonnative fish.