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13 Miller et al. (1982) concluded from collections of larvae and young-of-year below known spawning sites that there is a downstream drift of larval Colorado squawfish following hatching. Extensive studies in the Vampa and upper Green Rivers have demonstrated downstream distribution of young Colorado squawfish from known spawning areas (Archer et a1. 1986, Haynes et a1. 1985). Miller et a1, (1982) also found that young-of-year Colorado squawfish, from late summer through fall, preferred natural backwater areas of 0 velocity and less than I.S-foot depth over a silt substrate. Juvenile Colorado squawfish habitat preferences are similar to that of young-of-year fish, but they appear mobile and more tolerant of lotic conditions away from the sheltered backwater environment. While specific spawning locations have not yet been identified in the San Juan River, larval drift is presumed to occur. Adult Colorado squawfish were captured as far upstream as RM 163.3, while most young-of-year specimens were collected from backwaters in lower reaches of the San Juan River in the Utah portion of the study area (Platania 1990). Colorado squawfish were captured within the San Juan River in all seasons during which ichthyofauna1 surveys were performed (spring, summer, and fall) and are presumed to remain there during winter. A silt plug at the mouth of the San Juan into Lake Powell has impeded passage of Colorado squawfish since 1989. Within the rest of the Upper Basin, winter habitat for adult Colorado squawfish is generally characterized as relatively deep areas with slow-water velocity. Pools. backwaters, runs, shorelines, and eddies are all commonly used habitats during winter (Osmundson and Kaeding 1989, Tyus and Karp 1989, Valdez and Masslich 1989). Wick and Hawkins (1989) reported that during low- flow years on the Vampa River, pools and runs were used most frequently, suggesting that habitat availability influenced habitat selection by adult Colorado squawfish. The fish are largely sedentary during winter and exhibit only localized movement suggesting feeding activity. Very little information is available on the influence of turbidity on the endangered Colorado River fishes. It is assumed, however, that turbidity is important, particularly as it affects the interaction between introduced fishes and the endemic Colorado River fishes. Since these endemic fishes have evolved under natural conditions of high turbidity, it is presumed that the retention of these highly turbid conditions is an important factor for these endangered fishes. Reduction of turbidity may enable introduced species to gain a competitive edge, which could further contribute to the decline of the endangered Colorado River fishes. Areas of ImDact and Concern The San Juan River originates in the mountains of southwestern Colorado and flows southwesterly into the Navajo Reservoir situated on the Colorado/New Mexico border (Figure 2). Downstream of the Navajo Dam, the San Juan River continues westerly, flowing through the towns of Archuleta, Blanco, Bloomfield, Farmington, Fruitland, and Shiprock, New Mexico. It then turns north and :~ ~': ~::