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2 Dam which reached a maximum of approximately 97,000 cubic feet per second (cfs). Except . for the 1983 event, releases over the last 34 years have generally ranged between 1,000 cfs ' and 25,000 cfs, with flows averaging between 5,000 cfs and 20,000 cfs. As a result of the construction of Glen Canyon Dam, the Colorado River ecosystem below the dam has changed significantly from its pre-dam natural character. In addition, Glen Canyon Dam's highly variable flow releases from 1964 to 1991 caused additional concern over resource degradation resulting from dam operations. In October 1991, the Secretary adopted interim operations criteria which narrowed the range of daily powerplant fluctuations. Since the signing of the operating criteria in February 1997 (see Appendix A), these releases donot now exceed 25,000 cfs, and most often range between 10,000 cfs and 20,000 cfs. A NEED FOR SCIENTIFIC EVALUATION Responding to concerns that chlinges to the Colorado River ecosystem were resulting from dam operations, the Bureau of Reclamation (Reclamation) launched the Glen Canyon Environmental Studies (GCES) program in 1982. The research program's first phase (1982-1988) focused on developing baseline resource assessments of physical and biotic resources'. The second program phase (1989-1996) expanded research programs in native and non-native fishes, hydrology and aquatic habitats, terrestrial flora and fauna, cultural and ethnic resources, and social and economic itnpacts. Developing spatial and temporal data . using a Geographic Information System Was a critical part of the second phase. By the late 1980s, sufficient knowledge had been developed to raise concerns that downstream impacts were occurring, and that additional information needed to be developed to quantify the effects and to develop management actions that could avoid and/or mitigate the impacts. This collective information, and other factors, led to a July 1989 decision by the Secretary of the Interior (Secretary) to direct Reclamation to prepare an environmental impact statement (EIS) on the operation of Glen Canyon Dam. The intent was to evaluate alternative operation strategies to lessen the impacts of operations on downstream resources. In October 1992, the President signed into law the Reclamation Projects Authorization and Adjusnnent Act, Public Law 102-575. Responding to continued concerns over potential impacts of Glen Canyon Dam operations on downstream resources, Congress included the GCPA as Title 18 of the Reclamation Projects Authorization and Adjustment Act. Section 1802(a) of the GCP A requires the Secretary to operate Glen Canyon Dam: . . . in accordance with the additional criteria and operating plans specified in section 1804 and exercise other authorities under existing law in such a manner as to protect, mitigate adverse impacts to, and improve the values for which Grand Canyon National Park and Glen Canyon National Recreation Area were established, including, but not limited to natural and cultural resources and visitor -