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<br />. <br />a thin broM1 sediment covered the rocks. This genus is normally associated with <br /> <br />, <br /> <br />slightly stagnant water. In areas where the sediments became deeper than a few <br /> <br />millimeters, further reduction of the benthic fauna occurred and only insects <br /> <br />capable of surviving in an oxygen poor environment were present (for example, <br /> <br />Chironomus sp.). <br /> <br />Dissolved oxygen concentrations were not critical during the study period. <br /> <br />All measurements were above the six ppm level considered to be the minimum <br /> <br />concentration for trout. It is interesting to note that the greatest diurnal <br /> <br />fluctuations in D.O. (dissolved oxygen) occurred above De Beque,while the <br /> <br />highest nutrient levels were observed dOM1stream from the same location. It <br /> <br />is possible that changes have occurred in the animal and plant cOllllllllnities <br /> <br />downstream from De Beque. Rates of photosynthesis, reaeration, and respiration <br /> <br />may be different below De Beque than farther upstream. The Colorado River within <br /> <br />the study area may represent two distinct aquatic systems, one a cold, roily, <br /> <br />turbulent river and the other warmer and more placid. <br /> <br />Comparison of data. gathered during this study period to state water quality <br /> <br />standards now in affect show that the Colorado River is within limitations <br /> <br />assigned to the various river sections. From Dotsero to Grand Valley, the River <br /> <br />is designated BI' a cold. water fishery. From Grand Valley to Utah, the class- <br /> <br />ification is B2, a warm water fishery. <br /> <br />The Colorado River during the study period presented a paradox. The water <br /> <br />appears to be relatively clean. The presence of rapidly fluctuating fecal <br /> <br />coliform groups may indicate periodic enrichment due to man's activities. The <br /> <br />substrate of the River presents a nutrient enriched environment characterized <br /> <br />J <br />1 <br /> <br />-4- <br />