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the High Plains. The impacts on navigation from both depletion sources are summarized in table 3. At the 1975 level of water resource develop- ment without High Plains diversions, it was possible to maintain full service to navigation during 49 years of the 82-year record period. Service ranging between minimum and full was provided during an addi- tional 20 years. Minimum service usually involving shortened seasons was provided during the remaining 13 years. As depletions increased, the number of full-service seasons declined. Navigation was suspended in at least 1 year in all studies except the 1975 level base study. Substantial increases in the number of suspended navigation seasons were noted with diversions of 5.26 MAFA for all three levels of develop- ment. The diversion of 5.26 MAFA imposed upon the previously defined 2020 development level resulted in 38 or nearly 50 percent of the seasons in which navigation was suspended. At this depletion level, an 8-month season with full or partial service could be provided for only one-third of the years. Navigation on the lower Mississippi River would also be affected by diversion of water from the Missouri River because the Missouri furnishes a substantial portion of Mississippi flows during certain periods. These impacts have not been evaluated in this study, however. A significant impact would result on navigation and general recreational and environmental values along the Missouri River below Gavins Point Dam; however, sufficient water for irrigation, municipal and industrial water supply, and water quality would exist. Many of the water supply intakes would have to be modified to accommodate the lower water levels. Hydropower generation would also be affected by diversions of water from Lake Francis Case to the High Plains. The impacts on hydro- power generation are summarized in table 4. Of the total generator nameplate rating of 2,098 MW at the six main stem dams, 420 MW capacity, A19