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<br />II. WATER QUALITY' <br /> <br />\vater o.f the Uncompahgre River is of questionable quality since it <br />intercepts mine drainage containing'heavy metals upstream of Ridgway <br />Reservoir. The water quality generally improves downstream from mining <br />areas above' Ouray as the pH increases, from very acidic to alkaline, ' <br />causing the soluble metals to revert to a combined state and settle out <br />with the bottom sediments. <br /> <br />The Bureau of Reclamation in cooperation with the State of Colorado \ <br />and the U.S. Environmental Pr?tection Agency, ,is carrying out an intensive ,:',1 <br />pre-impoundment water quality monitoring program to supplement existing <br />data. This monitoring program will be continued after construction of <br />Ridgway Reservoir and will be u,tilized in developing operating criteria <br />for the project in cooperation with the State of Colorado and EPA. <br /> <br />, <br />J <br /> <br />Fishery Water Quality <br /> <br />The present stream fishery of the Uncompahgre River near the town of <br />Ridgway is considered .E.oor. The only sport .fishery in the river in this <br />area is maintained by an annual stocking of catchable rainbow trout. The <br />poor fishery is primarily because of the poor water quality of the river, <br />including extended periods of high turbidity. <br /> <br />The Dallas Creek Project with the Ridgway Reservoir would improv~ the <br />quality of \Vater do\Vnstream of the dam and thus improve the stream sport <br />fishery. The reservoir would function as a settling basin and thus reduce <br />downstream turbidity, a major factor now limiting the sport fishery. Also, <br />since impoundments and ponds have long been used for settling out mine <br />wastes and heavy metals, it is believed that Ridgway Reservoir would <br />similarly act as a sink for heavy metals and mine wastes which periodically <br />occur in the Uncompahgre River. <br /> <br />I <br />i <br /> <br />Concern has been expressed about the possible buildup of toxic sub- <br />stances in'the reservoir and the chance of passing these on downstream in <br />,quantities toxic to a'quatic .lHe. \Hth the proposed dual lev.el outlet, <br />whereby water can be selectively \Vithdrawn from near the reservoir surface <br />or near the bottom, this concern has been ~inimized. <br /> <br />The biological productivity of Rhlgw:lY Reservoir is predicted to be <br />only moderate. This is because of the water quality ~nd reservoir fluctu- <br />a tion, ~ <br /> <br />. <br /> <br />5 <br /> <br />r <br />