Rainbow trout are prized as a sport fish yet they could be a threat to the endangered humpback chub. However, some humpback chub find their way into the Colorado River making the area around the confluence of the Colorado and Little Colorado Rivers habitat for the largest population of humpback chub known today. Humpback chub readily reproduce in the Lower Colorado River because it is warmer than the Colorado River. Additionally, nonnative fish species like rainbow trout and brown trout compete with humpback chub for food and can prey on the chub. It is thought that Glen Canyon Dam has negatively affected humpback chub by restricting seasonal variation in flows, decreasing water temperature, and decreasing the amount of sediment in the water. Now this species is endangered with only six populations in existence. Humpback chub is a species only found in the Colorado River Basin. The increases in rainbow trout abundance in the 1990s may have been caused by changes in how the dam was operated, with less daily variation in flows starting in late 1990 resulting in increased survival of trout eggs and juveniles. Additionally, Glen Canyon, the approximately 15 mile stretch of river below Glen Canyon Dam, is a Blue Ribbon trout fishery. In fact, rainbow trout are now the dominant fish species in Glen Canyon and Marble Canyon, the stretches of river directly below Glen Canyon Dam. Continued stocking of rainbow trout ceased in 1998 because of an increase in the natural reproduction of rainbow trout near Glen Canyon Dam. Rainbow trout were introduced to the Colorado River below Glen Canyon Dam in 1964 as a sport fish. Endangered humpback chub caught near the confluence of the Colorado River and Little Colorado Rivers in Grand Canyon.
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