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12 Chapter S-Co/orado River Warer Quality Assessment l\:) ...... -.l C.D appear to be as great as previously found in the 1970's. The Colorado Department of Health has had a selenium health advisory posted for human consumption offish at Switzer Lake since the 1970's. There now appears to be a naturally reproducing fish population in Switzer Lake, in spite of continued elevated selenium concentrations in the fish tissue. Expanded and coordinated water quality studies in the GUnnison River are anticipated for several more years. Both acid mine drainage impacts to Ridgway Reservoir and downstream selenium concentrations from irrigation return flows will be the major focus of the studies to be conducted by Reclamation, the Task Group, and State of Colorado. The selenium issue may be closely related to salinity from irrigation. Dolores River Drainage High selenium concentrations have been found in areas near the Dolores Project. The study area may be receiving irrigation drainage from the project. The Dolores study area includes the project area and the lower San Juan River. Reclamation has sampled soils for new lands to be irrigated in the Dolores Project area and found only a few isolated cases of high selenium. These areas were eliminated from the project. The source of selenium in the San Juan River tributaries has not yet been determined. The San Juan River drainage may also he affected by oilfield produced brines which have been re-injected in shallow formations and are now re-emerging to the San Juan River and its tributaries. The Colorado River Water Quality Improvement Program studies are further investigating salinity impacts, including possible oil field re-injected brine sources. Sampling for the Task Group studies were initiated in the summer of 1990. Navajo (Upper San Juan River) The Task Group initiated reconnaissance studies of the upper San Juan River in 1990. The area is potentially affected by irrigation return flows from the Navajo Indian Irrigation Project, Hammond Project, and Fruitland Projects. In addition, there are possible impacts from oilfield brines and refineries and from a coal fired powerplant. Preliminary data from the study shows elevated polyaromatic hydrocarbons in fish tissues sampled. Significant contamination was reported at a field review conducted by the Task Group. Pine River Study The reconnaissance study of the Pine River was initiated in 1989. This study was initiated due to previous reports of selenium toxicity from well water in a very localized area during the 1960's. The Pine River Report should be published in 1991. No significant findings have been reported outside of the localized ground-water well contamination. MAIN STEM RESERVOIR QUALITY Each summer, the upper riverine reaches of Flaming Gorge Reservoir experience intense blooms of blue-green algae that seriously degrade the water quality for game fish and recreational boating. Evidence also exists that geochemical processes in the reservoir sediments affect both the intensity of the algal blooms and the salinity in the overlying water and that the algal blooms in turn iUlfect the geocheIr'.ical processes. At present, it is not known how effective restoration strategies, including external phosphorus and biological oxygen demand (BOD) loading reductions to the Flaming Gorge Reservoir, will be in reducing the intensity of the algal blooms or in increasing the dissolved oxygen concentrations in the water column. It is also not known how changes in the limnology of the riverine reach of the reservoir resulting from mitigative measures will affect fisheries and water quality in the downstream reaches of the reservoir or in the tailwater. Other reservoirs on the Colorado River were found to be nutrient poor in 1981 and 1982 [1]. Lake Powell and Lake Mead were oligotrophic