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Powell. The river crosses the Ute Mountain Ute and Southern Ute Indian Reservations and the Navajo Nation. Approximately 225 miles of the San Juan River are between Navajo Dam and Lake Powell; the lower 180 miles downstream from Farmington are designated as critical habitat for the Colorado pikeminnow and razorback sucker. Mean annual runoff in the river at Farmington just downstream from the confluence with the Animas River is 1.13 million acre- feet; near Bluff, Utah, this increases to about 1.25 million acre-feet. Below Navajo Reservoir, the San Juan River is joined by its major tributary, the Animas River, at Farmington before flowing westward to the Navajo Nation boundary west ofWaterflow, New Mexico. The river continues west and northwest before entering Colorado near the Four Comers landmark and flowing into Utah and then Lake Powell. The San Juan River for 7 miles downstream from Nav<0o Dam supports a high quality .trout fishery; from this point downstream for 10 miles to the Hammond Diversion a good trout fishery also occurs. Throughout the 35 mile reach from the Hammond Diversion downstream to Farmington, native fish populations increase as habitat becomes more favorable, although populations may be limited due to reductions in physical habitat related to now depletions. Nonnative fish such as carp and channel catfish become'common in this reach. The river between Farmington and Lake Powell maintains the most natural hydrologic conditions in the river, primarily due to the influence of the Animas River which is largely unregulated. This area is designated critical habitat for the Colorado pikeminnow and razorback sucker and supports other native fish such as the bluehead and flannelmouth suckers. Nonnative fish are common in this reach. The region south of the San Juan River is characterized by desert physiography; broad dry washes carry significant sediment loads during periodic thunderstorm events. The project area is semi-arid to arid; the major part of the basin is less than 6,000 feet in elevation and receives less than 8 inches of precipitation annually. Vegetation ranges from pinon-juniper areas around Navajo Reservoir to desert shrubs and grasses around the lower San Juan River. The San Juan River corridor supports riparian species such as cottonwood, willow, and nonnative salt cedar and Russian olive. Nonnative species dominate, with native willows and cottonwoods accounting for less than 15 percent of the riparian vegetation (Bliesner and Lamarra, 2000). The first 7 miles of the river downstream from Navajo Dam supports a significant riparian zone; this section of river is upstream from irrigation diversions so wetland vegetation receives water exclusively from the river. Approximately 2 miles of important wetlands developed immediately below the dam in areas used for construction borrow. On the 40 mile reach of river between Archuleta and Farmington, riparian areas have been impacted by agriculture, grazing, and commercial developments. Many of the wetlands in this area receive water from irrigation seepage and return flows. From Farmington to Lake Powell riparian areas of varying sizes and quality exist and are mainly dependent on river flows. Flows are more natural in this area, but riparian areas are impacted by livestock grazing and invasion by exotic plants. 5 .