The experimental flows are designed to benefit humpback chub, a fish species native to the Grand Canyon. The experiment will evaluate whether non-native trout are negatively impacting the endangered humpback chubs by competing for key habitat space and by preying upon the chubs. Additionally, the flows are anticipated to benefit the trout upstream in the 16-mile stretch from the dam to Lee Ferry by reducing the overpopulation of trout, thus increasing the viability and size of the fish. That stretch is within the Glen Canyon National Recreation Area and is managed for the sport fishery. The downstream river through Grand Canyon National Park is managed to benefit native fish species.

This is the second year of January-through-March high fluctuating flows. Releases will range between a daily high of 20,000 cubic-feet-per-second (cfs) to a low of 5,000 cfs. Researchers have discovered that since 1991, when such significant fluctuations were ended, the trout population dramatically grew at the probable expense of the native humpback chub population. Scientists are trying to determine if the fluctuating flows can keep the trout population in check by impacting their spawning and other aspects of their lifecycle.

Additionally, another ongoing experiment since last year has been the mechanical removal of non-native fish, primarily trout, near the confluence of the Little Colorado River and the mainstem Colorado River. The area is prime humpback chub habitat as the endangered fish move between both rivers. The removal effort, using electro-fishing techniques, reduces competition by physically removing trout. Early indicators from last summer's work have shown positive results.

Both experiments were analyzed in 2002 by an Environmental Assessment in accordance with the National Environmental Policy Act and were found to pose no significant environmental effects. The Bureau of Reclamation, the National Park Service, and the U.S. Geological Survey jointly prepared the study and are involved in the work. The experiments were proposed as a result of ongoing studies by the agencies and were recommended in 2002 by the Adaptive Management Work Group, a federal advisory committee to the Secretary of the Interior.