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UU.1/UU Revised Supplemental Draft Environmental Assessment-Chapter 3-Affected Environment anq Environmental Consequences Plateau Creek and the 5 miles of the Colorado River upstream to the Grand Valley Project Diversion Dam. The benefits of dam removal to endangered fish include (Nelson, 1999): 1. Only one fish ladder would be constructed instead of two. Multiple ladders tend to have cumulative effects on migrating fish. It would be easier and less stressful for fishes to migrate both upstream and downstream. During spawning migrations, adults would expend less energy reserves needed for spawning. Migration delays could adversely affect reproduction success. 2. Fish predators tend to congregate below dams. Downstream migration may result in mortality as endangered fish go over the dam spillway, become stunned and disoriented, and fall prey to predators. Removal of the Price-Stubb Diversion Dam would remove one of the spillways. 3. With the dam in place, there would always be a threat of hydropower development and associated impacts (entrainment, impingement, mechanical injury, and mortality). Fish that pass through power-generation turbines can be injured or killed. 4. Ladders result in fishes being concentrated in one place, which may result in predation, competition, and disease transfer. Fewer ladders may result in less predation on endangered fishes attempting to migrate upstream. The likelihood of moving greater numbers of fish upstream is better with one ladder than two. Reclamation concluded each fish passage alternative would have no effect on the humpback chub, and would complement efforts of the Recovery Program to stocked bonytail. The Colorado pikeminnow, razorback sucker, and their critical habitat may be adversely affected with nonnative fish access above the Price-Stubb Diversion Dam. During formal consultation regarding the Downstream Rock Fish Passage alternative, the Service identified selective fish passage at the Grand Valley Project Diversion Dam as a reasonable and prudent measure to reduce adverse effects on the endangered fishes and their critical habitats (Service, 2003). A copy of the Service's biological opinion is included in the appendices. Each passage alternative, excluding no action, would assure acces~ to critical habitat by the endangered fish to improve chances of their recovery. Instream construction activities would be avoided from May to September to minimize impacts to endangered fish spawning and larval development. Cultural Resources The area of potential effect for an investigation of cultural resource impacts extends along the Colorado River from Palisade to the Price-Stubb Diversion Dam. Prior to settlement and development of irrigation facilities, the area was part of the Ute Indian Reservation and covered western Colorado. After moving the Ute Indians to reservations in Utah and southwestern Colorado, Congress declared the lands public and open for 49