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the fish (Osmundson, D.B., U.S. Fish and Wildlife Service, personal communication, June 25, 1999). Burdick (1997) argues that habitat requirements on the Gunnison River have not been adequate for the survival of the endangered. fish. Some of the problems cited in this study are: • The depth below the Redlands Dam often dropped to less than 1 ft (Fig. 4). Indeed, flow ceased at times in this reach. Based on this finding, a minimum flow requirement of 300 cfs has been established to maintain I ft in depth at all times. • Flows of 15,000 cfs were common before the Aspinall unit was completed but have only occurred four times since the project was completed in 1965. The Aspinall unit has also caused a temperature decrease in the summer and increase in the winter. The most comprehensive view of habitat changes was conducted by Pitlick and co-workers (1999). Using data from unregulated rivers, the East River which flows into the Gunnison River and the Yampa River which flows into the Green River, they concluded that pre-1950 and post- 1950 annual peak discharges and mean annual discharges are not statistically different. Their study showed that changes to the Gunnison and Colorado Rivers were frequent and widespread, but that the period of the 1950s to 1970s was especially significant. Peak discharges and mean annual sediment loads were reduced significantly during this period. Because tributaries still contribute as much fine sediment as pre-1950, the lower flows now allow more sediment to deposit, causing the channel to become narrower and less complex. It is estimated that one-fourth of the sidechannel and backwater habitat has been lost in the Colorado since 1937 (Pitlick et al. 1999). Loss of habitat on the Gunnison River was not considered as severe by these authors. However, the Redlands Dam has prevented migration of the fish since 1918. Thus, pikeminnow might have spawned, drifted downstream, and then were unable to return. Indeed, the comment that pikeminnow were "never" abundant in the Gunnison (see Sect. 1) may be a result of the 1918 dam. In order to recover the pikeminnow and razorback sucker on the Gunnison, one researcher made the following comment: "Key to this restoration effort is recommending and implementing streamflows that will mimic the historical hydrograph to increase the magnitude and lengthen the duration of spring flows to create and provide riverine habitat for native fishes and at the same time control the smaller nonnative fishes in warmwater reaches of the Gunnison River." Razorbacks were then specifically mentioned as needing floodplain habitat-the need is for wetlands adiacent to the river corridor that were formerly inundated but no longer are (Burdick 1995). The appropriate floodplain habitat for razorbacks has been described as having a source of water other than the river itself with temperatures 5° to 10° degrees warmer. Such ponds would also be 5 acres or greater in surface area with a depth of 3 to 5 ft and a length of at least 1500 ft (WestWater Engineering hie. 1996). The overriding effect of habitat restoration may be evident based on observations related to re- operation of Flaming Gorge Dam on the Green River. Re-operation consisted of releasing flows that more closely mimicked historical circumstances. The number of pikeminnow encountered after re-operation was implemented is approximately three times what it was before. No effect