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<br />concentrations which are toxic to aquatic life. Excellent fisheries exist out- <br /> <br />side these mining areas and in the main stem through Monte Vista. Point sources <br /> <br />in the basin are a relatively minor problem. The agricultural impact on water <br />~ <br />~ quality within the closed basin Is significant but less serious than other <br />~ <br />~ areas of the State. The high water table In the basin results in many problems <br /> <br />being experienced with septic tanks. <br /> <br />San Juan Basin <br /> <br />The San Juan River drains a mountainous region in southwestern Colorado. <br /> <br />Durango is the largest town with a population of approximately 10,000. <br /> <br />The fishery resource varies from excellent in some reaches to poor in others. <br /> <br />Mining activities In the headwaters have caused metal and pH problems. Water <br /> <br />quality criteria for metals are violated on some segments. In the lower reaches <br /> <br />of the basin, suspended solids and salt problems are caused by irrigation on <br /> <br />moderately to highly saline soils. This river is considered to be an excellent <br /> <br />raw water source for drinking water. <br /> <br />Colorado Basin <br /> <br />The Colorado River drains the largest basin in the State, beginning hear <br /> <br />Granby in north central Colorado and flowing Into Utah west of Grand Junction. <br /> <br />Agriculture, mining, and tourism are the leading industries. <br /> <br />Sal inity is the most significant water quality problem in the basin caused <br /> <br />by irrigation on saline soils, natural salt sources, and salt concentration <br /> <br />owing to transmountain diversions and In basin consumptive uses, and inactive <br /> <br />mining operations cause metal problems In some mountain tributaries. These <br /> <br />metals degrade otherwise excellent fisheries and, in certain cases, violate <br /> <br />II - 4 <br />