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3 <br />• Subdivisions <br />The Upper Basin has been sub-divided by several investigators. <br />Joseph et al. (1977) divided basin streams into three groups according to <br />hydraulic and biotic conditions. Headwater reaches where temperatures were <br />suitable for salmonids were termed 'Trout Waters." Periphytic algae and benthic <br />invertebrate production is high in these reaches where clear water and rocky <br />substrates lead to a high level of primary productivity (Joseph et al. 1977). <br />Intermediate elevation reaches were termed 'Transition Zones" where water <br />temperature was intermediate between that optimal for Coldwater species and that <br />of warmwater species. Local fauna reflected the transition; salmonids were present <br />but cyprinids and catostomids were dominant (Joseph et al. 1977). Primary <br />• productivity was reported to be highest in this zone where water temperatures were <br />greater and total dissolved solids were higher than in the "Trout Waters." Water <br />clarity was sufficient enough to allow significant amounts of photosynthesis to <br />occur. Benthic invertebrates were reported to be very abundant except in areas of <br />sand substrate (Joseph et al. 1977). The lowest zone, where waters are suited to <br />warmwater species, was termed "Large River Channels". These were the large, <br />warm, turbid reaches, where primary productivity was greatly reduced due to low <br />water clarity. Benthic invertebrates were sparse since fine substrates dominated. <br />Allochthonous material was the major nutrient input to this zone (Joseph et al. <br />1977). The lowest zone is where the rare fishes live, although Colorado squawfish <br />n <br />U