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. . National Monument traveled at 0.06 to 5.6 kmph (Bauer et al. 1979). Specific conductance increased 14% between 1951 through 1979 in the Yampa River, presumably as a result of increased agricultural and municipal water uses (Wentz et al. 1980). The Yampa River was enriched with nitrogen but was low in phosphorous availability for algae. The invertebrate fauna indicate that the eastern portion of the stream is unpolluted, with high densities of Trichoptera and some Ephemeroptera (Boyle et al. 1984). Water quality in the upper Gunnison River is generally of high quality. The upper North Fork of the river had a mean TDS of 97 mg/L. Although trace-element concentrations were low, mean total iron concentrations were 8,250 mg/L, an effect attributed to local geology. Coal mining, which started in this basin in 1903, has elevated sulfate concentrations slightly, but altered overall water quality little (Norris 1987), while agricultural diversion has increased salinity. Concern over bioamplification of mercury and other heavy metals in fish tissues stimulated studies in Lake Powell during the 1970's (Standiford et al. 1973; Bussey et al. 1976). Tissue of four species of exotic fish were found to contain higher levels of naturally-occurring selenium than are recommended for human consumption (approximately 0.5 mg/kg). Mercury concentrations from the Navajop Power Plant and other sources was biologically amplified in fish tissues, but no fish over 2.0 kg exceeded public health standards for mercury (Potter and Drake 1989). By the time the Colorado River reaches tees Ferry, Arizona, it has drained 277,010 km of its 629,100 km basin. Kubly and Cole (1979) and Maddux et al. (1988) investigated river and tributary water quality from the Grand Canyon. The river water quality cations formed a "triple" water category: Ca++ (60% of milliequivalent total) > Na+ > Mg++ > K+ and anion concentrations were: . . . . . S04 > HC03 > Cl . . Kubly and Cole (1979) reported that Na+ dominated over Ca++ during March. Si averaged 8 mg/L, and the Colorado River at Lees Ferry had an ionic concentration of 605 mg/L which was five times greater than the world average for river water. Light transmittance exceeded 75%/m in the post-dam river when tributary inflow was at a baseflow level. The river water ~H ranged from 7.4 to 7.9, river water temperature ranged from 7 to 100 C at Lees Ferry. Mean phosphate concentration was 0.24 mg/L, with mean total N of 0.27 mg/L. Maddux et al. (1988) reported higher mean total N between 1984 and 1986, with 0.32 to 0.35 mg/L N03-N04 . 23 .