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<br />> . <br /> <br />31 <br /> <br />S1l t retards or stops aquatic plant growth by reducing the <br />amount and type of light. which passes into the water (Cole, 1941; Ingram <br />and Towne, 19~; Hynes, 1960). Settling particles blanket the stream <br />bottom SIIOther1ng plant and animal Ufe upon which fishes are dependent <br />(Cole, 19411 Ingram and Towne, 19~1 Hynes, 1960). <br /> <br /> <br /> <br />Hydrogen ion concentration <br />The pH values varied only slightly and only at the Gates of <br />Lodore study area ('rable 4). 3ince most fishes tolerate wide ranges <br />and rapid changes in pH (Lagler, 1956), fish distribution was probably <br />not aftected b,y hydrogen ion concentration. <br /> <br />Di ssol ved oxygen <br />Dissolved oxygen measurements ranged from 6.6 ppm at the <br />Gates ot Lodore study area to 8.6 ppm at Island Park (Table 4). <br />Averages varied trom 7.0 ppDl (75.9~ of saturation) at Gates of Lodore <br />to 8.4 ppm (84.5~ of saturation) at Island Park. The average dissolved <br />oxygen value on the Green River at Eoho Park was 7.6 ppm (84.3~ of <br />saturation). The higher values of dissolved oxygen at Echo Park may <br />have been due to the mixing effect of the rapids and ta11s in Lodore <br />Canyon. <br /> <br /> <br />Island Park had the widest range and average of all the <br /> <br />stations, probably due to the infiuence of rapids in Whirlpool Canyon, <br /> <br />increased aquatic plant life, and lower water temperatures during <br /> <br />September when the determinations were made. All measurements of <br /> <br />dissolved oxygen suggest that the fish fauna was not limited in <br /> <br />distribution by this factor. <br /> <br /> <br />