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14 <br /> flooding of roads and fields, and plugging of water intake systems <br /> for the mines. <br /> The capability of a stream to maintain indigenous fish populations <br /> is jeopardized when factors extrinsic to natural degradation are intro- <br /> duced. These factors become critical only when the tolerance level for <br /> a fish species is exceeded. <br /> Excepting flood-producing rainstorms in summer, runoff is dominated <br /> by snowmelt which creates high discharges generally between early May <br /> and the end of July. , Peak discharge at Stonewall during this period was <br /> about 65 and 80 cfs in 1978 and 1979, respectively. Very low flows were <br /> recorded from mid-September to mid-April each year, with minimum flows <br /> being 4 cfs at Stonewall . These periods of low flow are of most concern <br /> when considering welfare of fish. This is because of the reduced <br /> capacity for dilution of any toxic or harmful effluents introduced into <br /> the stream. <br /> Water quality is monitored at a USGS surface water gaging station <br /> at Stonewall , Colorado on the Middle Fork approximately 4 miles upstream <br /> from the Allen Mine. Measurements of water quality parameters at this <br /> station were averaged in the Water, !taste & Land, Ltd. (1980) report. <br /> Of the chemical parameters reported, only a few can be related to the <br /> Welfare of fish populations. Measurements of suspended solids and <br /> turbidity, which may be of more consequence to the production of fish, <br /> are not available from USGS. <br />