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Although a single sampling precludes a precise and indepth analysis <br />• of the aquatic macro invertebrate fauna in the Williams Fork River, a few <br />general observations can be made. The fauna consist largely of macroin- <br />vertebrate taxa which are intolerant or facultatively tolerant of organic <br />pollution. There appears to be a relatively high standing crop (density) <br />and species diversity. Many of the species collected such as Baetis <br />spp., Tricorythodes sp. (mayflies), Isogenoides sp. (stoneflies), hydro- <br />psychid caddisflies and certain dipterans are tolerant of environments <br />with relatively high silt loads. In general, the numbers and kinds of <br />invertebrates are characteristic of a moderately silt-stressed western <br />scream. Based on the ecological requirements of the organisms, other <br />types of pollutional stresses (e.R. organic enrichment, toxic metals <br />etc.) are not apparent. Differences in total densities between stations <br />• are probably due more to heteroRenous distribution of the various macro- <br />invertebrate Qroups rather than to any identifiable stresses in the <br />area. $owever, as emphasized at the beginning of this section, no <br />definite statements can be made about the condition of the river based <br />upon a single sampling. Additional sample periods during the spring and <br />early summer are recommended to identify any seasonal differences in <br />composition and abundance. <br />• <br />7 <br />