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the reservoirs. As shown, after Pathfinder Dam was built, average yearly peak flowed declined by 50%, while average flow declined by only 18%. And yet, after McConaughy and Seminoe were added, both peak and average flow dropped by about 70% j after Glendo, both peak and average flow increased by about the same percent. In each case, the decline measured in absolute terms rather than percentages was much greater for peak flows. Of course, at 104 000 acre-ft Grayrocks Reservoir is considerably smaller than any of those listed in Table Ij moreover, the Laramie contributes only about 17% of the flow of the North Platte at the state line. Accordingly, the averaging effects of this reservoir on peak flows in the North Platte are likely to be small. On the other hand, Lake McConaughy, the largest of the four reservoirs of Table I, lies between Grayrocks and the critical habitat. If flows into the lake are reduced, average reservoir level will drop, provid- ing more room to store peak flows. Thus, even if the operating rules of Lake McConaughy remain unchanged, peak flows may well decline more than average flows, even on a percentage basis. To summarize, the completion of MBPP is likely to reduce average flows in the critical habitat by about 3%. The reduction in peak flow is difficult to determine, both in absolute and percentage terms. Such a decline in flow rate at first glance does not seem very significant, especially because of the sub- stantial variation already found in daily flows. However, Grayrocks is only one of several planned projects that use water from the Platte River, and the cumulative effect of these other projects in addition to Grayrocks was an important issue in the case. The proper way of dealing with this question of cumulative effects is beyond the scope of this section, but we will return to it later. 3. Reduced flows in the Platt~ will allow the encroachment of tall vege- tation in the channel of the river. Unquestionably, the past century has seen a severe decline in the channel width of the Platte. Large areas over part of the Platte River channel once nearly devoid of vegetation are now overgrown with shrubs and young cottonwood trees, and are on that account unsuitable habitat for both sandhill and whooping cranes. On the basis of old photographs and the measurements of 19th century explorers, Williams (1978) has estimated that current channel widths at various points are only 5 to 40% of what they were 80 to 100 years ago. These declines have been particularly severe up- stream of the critical habitat. At Brady, for example, the decline has been 36