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134 The river between Fannington and Lake Powell maintains the river's most natural hydrologic 135 conditions, primarily due to the intluence of the Animas River which is largely unregulated. 136 This area is designated critical habitat tor the Colorado pikeminnow and razorback sucker and 137 supports other native fish such as the bluehead and tlannelmouth suckers. Non-native fish are 138 common in this reach, particularly downstream from the Public Service of New Mexico (PNM) 139 diversion dam. 140 The San Juan is similar to other rivers in the upper Colorado River Basin with large tlows during 141 spring snowmelt followed by low (base) tlows the rest of the year; however, summer and fall 142 spike tlows occur due to thunderstorm events to a greater degree than in other rivers. Following 143 Navajo Dam construction, spring peaks were reduced by nearly half and base tlows increased 144 (Bliesner and Lamarra, 2000). In general, upper reaches of the river are cobble-dominated and 145 lower reaches are sand-dominated; much of the lower reaches are canyon bound. Summer water 146 temperatures have been lowered in the upper reach of the river due to Navajo Dam'releases. 147 Sediment intlow to the river is significant during summer and fall thunderstorms-there is 148 historical evidence that this was much greater around the turn of the century, when there was 149 rapid erosion of the watershed due to overgrazing or other factors, In the 20'h century there was 150 also a large invasion of non-native vegetation into the river's riparian area. Overall, the 151 combination of accelerated erosion in the watershed, invasion of non-native plants, and 152 regulation of flow by Navajo Dam has probably created a quite different river environment than 153 occurred 150 years ago. 154 The first 7 miles of the river downstream from Navajo Dam supports a significant riparian zone; 155 this section of river is upstream from irrigation diversions so wetland vegetation receives water 156 primarily from the river and tributary groundwater. Important wetlands have developed in areas 157 formerly used for construction borrow along the river, extending approximately 2 miles 158 downstream from the dam. On the 40 mile reach of river between Archuleta and Farmington, 159 riparian areas have been impacted by agriculture, grazing, natural gas development, and 160 commercial developments. Many of the wetlands in this area receive water from irrigation 161 seepage and return flows. From Farmington to Lake Powell, riparian areas of varying sizes and 162 quality exist and are mainly dependent on river flows. Flows are more natural in this area, but 163 riparian areas are impacted by livestock grazing and invasion by non-native plants. The San Juan 164 River corridor supports riparian species' such as cottonwood, willow, and non-native tamarisk 165 and Russian olive. Non-native species dominate, with native willows and cottonwoods 166 accounting for less than 15 percent of the riparian vegetation (Bliesner and Lamarra, 2000). 167 The region south of the San Juan River is characterized by desert physiography; broad dry 168 washes cany significant sediment loads during periodic thunderstorm events. The project area is 169 semi-arid to arid; the major part of the basin is less than 6,000 feet in elevhtion and receives less 170 than 8 inches of precipitation annually. Vegetation ranges from pinon-juniper areas around 171 Navajo Reservoir to desert shrubs and grasses around the lower San Juan River. 6 00655