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114 115 .. Water Quality Neel (1963) has pointed out that reservoirs may have no reasonably predictable pattern of limnology. In western reservoirs. erosion of silt. clay and sand fills the reservoir at a fast rate (figure 5). Workman and Keith (1974) concluded that erosion control or management in the Upper Colorado River Ba81n W01!ld be ineffective from the physical and biological standpoint and would also be unsound from an economic standpoint. Although the building and regulation of reser- voirs provides greater quantities of water for uae. reservoirs also reduce total runoff by exposing more surface for evaporation (Neel. 1963). In addition. the porous sandstone of the Lake Powell Basin absorbs much water and further reduces the amount that flows downstream in the Colo- Sedimentation is considered by the U.S. Geological Survey to be one of the more important pollutants in streams. These sediments result from land uses that denude soils. Logging (Gibbons and Sa10. 1973; Hall and Lantz, 1969). stream channelization (Elser. 1968), improper watershed management (Platts and Megahan, 1975), and grazing (Gunderson, 1968; Lusby, 1970; Platts, 1958) all contribute to increases in sedimentation. Increases in fine sediments in spawning gravel related to logging prac- tices decreased the survival of salmonid eggs in an Oregon stream (Hall and Lantz, 1969), In the Strawberry Reservoir drainage of north-central Utah, mortality of the eggs of the cutthroat trout (Salmo clarki) was 45 percent in the pre-eyed stage and 30 percent in the eyed stage from a stream where heavy grazing occurred versus 29 percent and 4,5 percent for rado River. Symons, Weibel, and Robeck (1964) reviewed the influence of impoundments on water quality and prOVided recommendations for research. In addition. the effect of water level fluctuations on fish and other aquatic organisms is covered by the bibliography of Fraser (1972a). Other investigators reported the effects of new impoundments, such as those on the Green River and its tributaries, on aquatic life (e.g., Funk and Gaufin, 1971; Varley, Regenthal, and Wiley, 1971). .' ... ., respective stages in a section of the same stream where grazing was less "', .. <; intense (Platts, 1958). The experimental addition of sand to a Michigan I( ... stream increased the gradient and width of the stream and reduced the '" .. .. depth and pools (Hansen and Alexander, 1976), Such physical changes in 1968; Etnier, 1972; Lewis, 1969; Ward, 1976). In the arid and semiarid A water quality assessment has been recently made for the Colorado " '" , .- ",' .. .. "' '" .. a stream can have pronounced impacts on the biota of the stream (Elser, common but the effect of this turbidity on the fish inhabiting this river River (Utah Water Research Laboratory. 1975). This comprehensive study (over 1.200 pages) is too detailed to summarize here; it is noteworthy. however, that the study has demonstrated that salinity is the major water quality factor in the basin. and its interactions outweigh all other con- siderations except the availability of the water resource. Average total salinity of the Colorado River system in 1972 was less than 50 mg/l in the headwaters but increased to 847 mg/l at lmperia1 Dam in California (Bessler. 1975). Several pieces of federal legislation are directed at area of the Upper Colorado River Basin, turbidity caused by sediments is system is not known. Some studies have indicated that turbidity can affect the behavior of fish (Heimstra, Kamkot, and Benson. 1969). Sedimentation is particularly important in reservoirs (Dendy, 1968) where suspended materials settle because of decreased velocities, The net result is that reservoirs become f~lled. limiting their life spans.