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. . 0417 The U. S. Forest Service has participated in either formulating or reviewing the pollution abatement criteria to be utilized during construction of the facilities and will be requested to review the specifications before issuance. 2. Bio logi cal a. Construction.--Some minor adverse impact may result to the marine biology in Twin Lakes from increased turbidity which may occur during the time required to construct a temp crary Highway 82 detour around the powerplant c.:cc.struction site. Houever, the contractor will be required to minimize the amount and duration of turbidity. The lake side of the detour will be protected from wave action by ripI'ap or cobble. Return flows of water purr.p~d frcm the powerplant excavation during de- watering and drainage from the contractor's work area will be filtered through an earth settling pond and treated as required so that these flows will not degrade Twin Lakes water. The Bureau of SPOI't Fisheries and Vlildlife and Colcrado GalCie, Fish and Parks will be requested to review the specifications and I'ecr,nimend criteria required to prevent or minimize stl-'eam or lake pollution from construction activities. B. Operac'r.n.--Very little is known about the effects v't, Elbert Powerplant operation and pump-back storage wi,_l have on the marine life of Twin Lakes. 1. Ecological.--The physical and biological environment of Twin Lakes is not native but one that has been manipulated by man to improve the fishery. Twin Lakes was constructed and is operated primarily for irrigation water storage and fishery management is secondary. Lake Trout (Mackinaw) were planted in the early 1920's and managed for a prize fishery. Lake Trout have been taken the.t measured 42 inches long and weighed 32 POUr.d0' L2rge Brown Trout, Rainbow and Kokanee Salmon have also been taken. T,lin Lakes supports one of a few mysid shrimp populations in the Western [Jr,i ted States and the only one in Colorado. ~Iysid shrimp are excellent trou~ food and may be an important factor in the successful trout fishery in Twin Lakes. Mackinaw feed on the shrimp until they grow to about 20 inches in length, they then feed on other forage fish, includ- ing Bonneville-cisco, another introduced species. We don't know what effect the powerplant opeI'ation will have on lake temperature and oxygen content. Water temperatures above 600 F have been determined to be toxic to mysid shrimp. Eowever, we do not anticipate that the water temperature w.ill rise dbov~ EOo F. The preservation of lake trout spawning habitat in Twin Lakes Reservoir is of cons iderable importance to the tho\18ands of fishermen who go there. 4