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nOZ437' This management plan is intended to offset impacts to the endangered fishes due to existing and I, certain new depletions from the Yampa River Basin in Colorado and Wyoming. It anticipates that new depletions would result from direct-flow diversions, small tributary reservoirs and/or modest expansion(s) of existing reservoir(s). Although the plan considers impacts to the Green River due to depletions from the Yampa River, it does not address impacts of depletions from the Green River mainstem or any of its tributaries other than the Yampa River. Total existing and future depletions, representing an estimated 15% of the average annual yield of the Yampa at its confluence with the Green River, are expected to have a modest impact on peak flows. The Recovery Program will implement management actions described below to offset depletive impacts to base flows, minimize impacts to peak flows, and reduce impacts due to competitive and predatory nonnative fishes. To implement these actions, the U.S. Fish and Wildlife Service (Service) and the States of Colorado and Wyoming, as partners in the Recovery Program, intend to sign a Cooperative Agreement to implement the various elements of the plan. The Recovery Program will incorporate these elements in its Recovery Action Plan, establish schedules to initiate and complete recovery actions described herein, and fund and implement these actions, subject to appropriations, except as noted below. The Service recommended that daily average base flows in the Yampa River not fall below 93 cubic feet per second (cfs) at Maybell from August through October at any greater frequency, magnitude or duration in the future than had occurred historically (Modde et aL 1999). Historical records show that base flows at Maybell occasionally have fallen below the 93-cfs flow target in July, as welL Therefore, the base-flow period was expanded to include July. Moreover, uncertainty with respect to the winter flow needs of the fishes prompted the Service to extend the base-flow period through the winter months (November-March) with a 33% buffer added to the 93-cfs flow target (i,e., 124 cfs) during this period, which is consistent with observed hydrologic patterns. This plan proposes to augment base flows in accordance with these recommendations to compensate for impacts to base flows due to depletions. Hydrologic modeling demonstrated that 7,000 acre-feet (AF) would satisfy base-flow needs in all but the driest years. In developing this plan, 13 base-flow augmentation alternatives were identified and evaluated. Alternatives include both structural and non-structural options, which rely upon one or more of the following six potential sources: 1. Supply interruption contracts (3,700-7,000 AF) 2. lnstream flow water rights (up to 7,000 AF) 3. Steamboat Lake (2,000-7,000 AF by lease) 4. Elkhead Reservoir (3,700-7,000 AF by lease, exchange and/or enlargement) 5. Stagecoach Reservoir (1,300-7,000 AF by lease, exchange and/or enlargement) 6. New tributary reservoir(s) (up to 1,300 AF total) Structural alternatives include both single-source and multiple-source options. Each of 13 action alternatives was subjected to a preliminary feasibility analysis, using the following evaluation criteria: (I) ability to meet base-flow needs; (2) estimated cost; (3) impacts on Colorado State Parks and water-related recreation therein; (4) impacts on agriculture; (5) impacts on peak flows; and (5) legal and institutional constraints. Based on this analysis, an enlargement of Elkhead Reservoir provided the most reliable supply at a moderate cost. with minimal impacts to parks and water- related recreation, agriculture and peak flows. Steamboat Lake and Stagecoach Reservoir alternatives, as well as combinations with these reservoirs, were somewhat less reliable, and caused greater impacts to park and recreation and peak flows, ~ Management Plan for Endangered Fishes in the Yampa River Basin XVlll