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l Ward et al. (1980) -studied Che effects of acid mine drainage on ~~ macroinvertebrate communities in Trout Creek located in northwestern Colorado. The study found that macroinvertebrate populations were not affected by the acid mine drainage, as density and composition were similar above and below the effluent. Generally low values of sulfate and iron, highly-buffered waters, and low levels of toxic substances minimized nay adverse effects of acid inputs. A buffer strip between mine spoils and the stream also contributed to stable conditions. The only problems identified is the stream were increases in salinity, sedimentation, and water depletion. Wentz (1974) also concluded that coal-mine drainage is not a significant problem in Colorado streams. Streams in western energy-development areas generally exhibit pH values between 7.0 and 8.0 (Skogerbee 1976). Waters are well buffered and major inputs of acid or base would be required to shift the pH one or mare units (Ward et al. 1978). The potential effects of constructing and operating a coal silo for Empire Energy's underground mine near Craig, Colorado on aquatic resources is the Williams Fork River were evaluated is this survey. Although runoff from the mined area may carry elements contained in mine spoils into the river, ao zone of influence was observed (ie. lowered pH, presence of ferric hydroxide precipitate). Thus, the primary potential problem is increased sedimentation, as a result of construction of the silo and runoff in areas covered with mining spoils or coal. Accumulation of silt oa rock surfaces can affect the development of benthic macroinvertebrates by limiting feeding and respiratory functions. Certain species of benthic organisms such as mayflies and caddisflies are sensitive to siltation and often are lacking from waters with high silt levels (Wilber 1969). In addition, excessive siltation also could remove important habitat for fish or interfere with respira- tion or ocher life functions. Construction activites also can reduce bank stability which could alter flow patterns, increase sedimentation, and remove fish habitat. Although sediment was visible on rock substrates in the study area, it did not Limit benthic macroinvertebrate production. In general, macroinvertebrate abundance and composition was similar above and below the coal silo. Ia addition, benthic macroinvertebrate groups 12