Nonnative Fish

Closeup pf a striped fish being held by the mouth. Man in the background in a tank top.

Trash Trackers/NPS Photo

Drawing of a striped bass.
Striped bass (Morone saxatilis)

Nonnative Fish in Lake Powell

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.

Today, Lake Powell is recognized as having one of the best sport fisheries in the country. Anglers travel great distances to enjoy the remarkable scenery and the unlimited take of striped bass. Angler harvest of striped bass helps keep their population, which is prone to booms and busts, healthy. Other species are targeted as well, including walleye, which can have negative impacts of native fish.

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.

Drawing of colorful fish
Rainbow trout (Oncorhynchus mykiss)
Nonnative Fish in the Colorado River below Glen Canyon Dam

Rainbow trout (Oncorhynchus mykiss) were stocked in the water released from the dam in the Lees Ferry area in the 1970’s. Native fish are unable to reproduce in the cold water released from the dam, but rainbow trout have flourished. Now, the 15-mile stretch from the Glen Canyon Dam to Lees Ferry is a world-famous rainbow trout fishery.

In 2014, Glen Canyon NRA and Grand Canyon NP collaborated with partners, especially Arizona Game and Fish, to develop the Comprehensive Fisheries Management Plan. This plan established goals and evaluated alternatives to managing the rainbow trout fishery to keep the population healthy, with high catch rates and large fish, while also protecting and enhancing native fish populations in Grand Canyon.

In recent years, the brown trout populations have expanded in the Lees Ferry reach to levels much higher than seen in the past. Brown trout are predatory on rainbow trout and are demonstrated to have negative impacts on native fish, including the endangered humpback chub. Examples exist where brown trout have displaced rainbow trout fisheries. More information on the management of brown trout to save the rainbow trout fishery is available at the Lees Ferry Fisheries Monitoring link below.

Green sunfish exist in Lake Powell and occasionally survive passing through the dam. Green sunfish are highly predatory and have been shown to impact native fish populations in other waters. Some backwater areas in the river below the dam warm in the summer enough that green sunfish can reproduce. The NPS has partnered with other agencies to removed green sunfish populations in backwaters and develop long-term strategies to prevent green sunfish and other non-native warm-water fish from establishing below the dam and impacting native fish.

The river below the dam and into Grand Canyon is considered sacred by several Native American tribes. Fisheries management activities can be offensive, especially when many fish must be killed. To mitigate the negative tribal impact from taking fish in management actions, the NPS and partners identify beneficial uses for the removed fish. Most commonly the fish are provided to a tribal aviary to feed injured eagles.

Last updated: January 19, 2017

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Mailing Address:

PO Box 1507
Page, AZ 86040


(928) 608-6200
Receptionist available at Glen Canyon Headquarters from 7 am to 4 pm MST, Monday through Friday. The phone is not monitored when the building is closed.

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