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. . . Lt. Colonel Dorothy F. Klasse 6 potential for young Colorado squawfish and razorback suckers. Any additional large loss of water or further degradation of remaining habitats of the San Juan River will exacerbate problems the Colorado squawfish and razorback sucker are currently experiencing in the San Juan and other subbasins throughout the Upper Basin. Water Qualitv Surface and ground water quality in the Animas. La Plata. Mancos. and San Juan River drainages have become significant concerns (Brogden et al. 1979). Potential heavy metal and/or selenium contamination in project-affected rivers and newly created reservoirs and the subsequent bioaccumulation in the food chain could become a problem for the predatory Colorado squawfish. as well as the razorback sucker. Changes in water quality and contamination of associated biota are known to occur in similar Bureau projects in the San Juan drainage (i.e.. irrigated lands on the Pine and Mancos Rivers) where return flows from irrigation make up a portion of the river flow or other aquatic sites downstream (Sylvester et al. 19B8). Increased loading of the San Juan River and its tributaries with soil salts. elemental contaminants. and pesticides from irrigation return flows could potentially degrade water quality and cause harm to the endangered fishes. . Turbiditv 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. Because these endemic fishes have evolved under natural conditions of high turbidity. it is concluded 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. Colorado Souawfish Historical and Current-Distribution The Colorado squawfish evolved as the main predator in the Colorado River and San Juan River systems. The diet of Colorado squawfish longer than 3 or 4 inches consists almost entirely of other fishes (Vanicek and Kramer ~ \ "