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Executive Srnnmary alternatives, it is unlikely that they would alter the relative ranking of the fluctuating and steady flow alternatives, GAO also found that Reclamation generally used the best available data in making its impact detenninations. For example, for information on cultural resources and properties, Reclamation went beyond the federal requirements for the development of an impact statement by performing assessments of all previously identified archeological sites within the Colorado River corridor in the Glen and Grand canyons, According to many experts, when completed, this effort generated the best and most current scientific information available. However, GAO also found some limitations in the data used in the development of the impact statement. Specifically, some of the information was dated, some was preliminaIY, and some was incomplete, For example, to assess the economic impact of the alternative flows on recreational activities, Reclamation used a 1985 survey of a sample of anglers, day-rafters, and white-water boaters that asked about their experiences on the Colorado River and what effect, if any, different streamflows would have on their recreational experiences, Although Reclamation updated some of the data to 1991, it acknowledges that the survey information is generally dated, The National Research Council generally found the analysis to be adequate, Many of the results of the sediment studies at Glen Canyon were preliminaIY, were in draft form, and had not been published at the time that the draft or even the final impact statement was written, However, according to the researchers that GAO interviewed, no new or additional information on sediment impacts has been obtained that would alter the information or conclusions presented in the final impact statement. Finally, the information on some resources is incomplete, as is the knowledge of how changes in the Glen Canyon Dam's operations will affect those resources, For example, in part because of incomplete data, the experts' opinions VaIY on the interactions between native and nonnative fish and how operational changes would affect these interactions and, ultimately, fish populations, In its final biological opinion, the U. S, Fish and Wildlife Service stated that Reclamation's preferred alternative for the dam's future operations, the Modified Low Fluctuating Flow alternative, is likely to jeopardize the existence of two native endangered fish species (the humpback chub and the razorback sucker). The Service identified actions that would modify the preferred alternative with seasonally aQjusted steady flows, The Service and Reclamation agreed to categorize these flows as experimental, or research Page 7 GAOIRCED-97-12 Glen Canyon Dam's Environmental Impact Statement