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Implementation of the Yampa Plan may result in certain environmental, social, and economic <br />effects: <br />Tyus and Saunders (2001) consider the Yampa River to be the most valuable tributary in the Upper <br />Colorado River Basin in terms of its contributions, both direct and indirect, to the recovery of the <br />four endangered fish species. It supports populations of Colorado pikeminnow and humpback chub, <br />and provides spawning habitat for razorback sucker. It also provides volume and shape to the Green <br />River hydrograph and delivers sediment to the Green River necessary for creating and maintaining <br />floodplain nursery habitats for Colorado pikeminnow and razorback sucker. <br />The principal impact of the proposed action is a year-round reduction in stream flows due to current <br />and projected future water depletions of roughly 240,000 AF. Because new reservoir storage is a <br />relatively minor component of the proposed action and water demand peaks after spring runoff, <br />impacts to peak flows should not be significant. However, without mitigation, impacts to base flows <br />would be significant. A reduction in base flows, in turn, could aggravate existing localized water <br />quality problems, due to higher temperatures, lower dissolved oxygen and higher concentrations of <br />pollutants from outfalls of wastewater treatment facilities or mine drainage. A water demand study <br />(BBC 1998) projected full-time residential population growth by 2045 of 90-134% relative to the <br />2000 census, which will increase the volume of domestic wastewater discharged to the river. <br />However, wastewater facilities are expected to be expanded to handle the additional wastewater <br />load. <br />Except for the site of the Elkhead Dam enlargement, impacts to wetlands, riparian vegetation and <br />their associated wildlife communities should not be significant. Impacts due to the enlargement of <br />Elkhead Reservoir would be mitigated. No impacts to upland vegetation or wildlife are expected to <br />result from the proposed action. <br />Native fisheries should benefit from the proposed action due to the augmentation of base flows and <br />expected reduction in predatory and competitive nonnative fishes. Conversely, sport fisheries within <br />the Yampa River will be adversely affected by nonnative fish control activities designed to reduce <br />the nonnatives' predation on and competition with endangered and other native species. However, <br />public access to the Yampa River is limited because it borders private land, and many sportfish <br />removed from the river will be translocated to local ponds and reservoirs where they would be more <br />readily available for anglers to harvest. Therefore, the fishery resource will be preserved for public <br />use. Nevertheless there would be a negative effect on the river float-fishing experience. <br />Measures to mitigate and/or minimize adverse effects have been incorporated into the proposal. <br />Measures to mitigate the effects of depletions on endangered and other native fish species include <br />base-flow augmentation, nonnative fish management, habitat restoration, stocking endangered <br />fishes, and monitoring the effects of depletions and the aforementioned mitigation measures. <br />Although Elkhead also will serve human water needs, the principal objective of enlarging the <br />reservoir is to provide a firm water supply to augment instream flows during the base-flow period. <br />Finding of No Significant Impact 5 <br />