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n02611 2. Possible environmental effects of the massive transfer of. water'frbm the northern part of C'alifornia; 3. The effects of continued overdraft of ground- water; 4. The deterioration of terminal lakes resulting from increased depletion of tributary stream- flow; and 5. The degradation of water quality with more intensive use. The first of these problems affects all regions; the second affects the California Region. The third affects the Lower Colorado Region primarily, has affected the California Region also, and may continue unless the massive transfer of water is accomplished. The fourth affects the western part of the Great Basin Region; and the fifth affects all regions. Many of the problems of apportionment and utilization of the waters of the Colorado River Basin were settled between 1922 and the present by negotiation, legislation, Federal administrative action, and litigation; but important problems remain. There is a difference of opinion between the Upper and Lower Basin States concerning the items that are to be taken into account in computing the surplus water available for meeting treaty requirements for delivery of 1.5 million acre-feet to the Republic of Mexico. The controversial items are the accounting of con- sumptive uses within the basin, the gains and losses below Lee Ferry - the contribution of tributaries, evaporation from reservoirs - and losses (estimated to be about 300,000 acre-feet per year) incurred in conveying the required quantity from Lee Ferry to Mexico. The commitment for delivery at Lee Ferry is at ieast 7.5 million acre-feet per year averaged over a lO.year period, and, according to some interpreta- tions, it may be as much as 8.25 million acre.feet plus a share of the iosses incurred in delivery of water to Mexico. In the Colorado River Basin Project Act (p.L. 90-537), the United States Congress declared that " . . .the satisfaction of the requirements of the Mexican Water Treaty from the Colorado River constitutes a national obligation which shall be the first obligation of any water augmentation project planned pursuant to Section 201 of this Act. . . ". If such augmentation is sufficient to meet the de- ficiencies created by the Mexican Water Treaty, judicial interpretation of the controversial points may never be required. The depletion requirements for water from the Colorado River Basin above Lee Ferry projected to 2020 are about 6.5 million acre-feet (4.9 within the basin and 1.6 exported). Most of this would be reflected in depletion of streamflow at Lee Ferry. Consequently, the projected depletions are feasible only when enough water is available to satisfy them, Water Resources without depleting the flow at Lee Ferry more than allowed by the Colorado River Compact. Current usage accounts for much of the nearly complete utilization of the Colorado River, when the mean virgin flow at Lee Ferry is near the level at which it has been for the last 40 years, with the balance of usage caused by. the initial fIlling of Upper Basin reservoirs. Hence, the projected depletion is de- pendent on the long-term mean virgin flow which is greater than the mean since 1930, or on augmenta. tion of the Colorado River flow. The basic apportionments of water from the main stem of the Colorado River below Lee Ferry are 2.8 million acre.feet for consumptive use in Arizona, 4.4 million for California, 0.3 million in Nevada, and 1.5 million for Mexico. Adding losses of 1.6 million (estimated for 2020) from the river and main stem reservoirs makes a total requirement of 10.6 million, of which about 0.8 million acre-feet would be supplied by tributary inflow below Lee Ferry. When Upper Basin depletions reach the projected level (6.5 million), augmentation will be required to meet the foregoing Lower Basin requirements. Although the basic allotments described above combined with upstream depletions exceed the natural yield of the Colorado River Basin, they are not sufficient to meet requirements. California is currently using surplus water in addition to its basic apportionment because Arizona and Nevada do riot have facilities for full utilization of their shares. Nevada has completed the first stage of the Southern Nevada Water Project and is delivering water from Lake Mead to Las Vegas and the surrounding area. With completion of the final stages of the project and the Central Arizona Project facilities, California wlll have to reduce its annual consumptive use of Colorado River water from 4.9 to 4.4 mlllion acre-feet. Arizona has chosen to use part of its share in the Phoenix- Tucson area where the 1965 overdraft of ground- water was about 2.5 million acre.feet. New imports to the area will reduce but not eliminate the overdraft even with no increase in water use. The development of streamflow in the northern part of the California Region to meet requirements involves a large increase in surface storage capacity (from 27 to 106 million acre-feet) and massive transfers of water from north to south. Considerable opposition to such storage and diversion has de. veloped because of possible environmental effects in the northern river basins and in the Sacramento River Delta and San Francisco Bay. Increasing water requirements in the Great Basin Region generally can be met by more intensive use of streamflow, greater use of groundwater, and increased imports from the Colorado River Basin, provided that no attempt is made to maintain Pyramid and Walker Lakes. If Pyramid and Walker Lakes are to be 25