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streams. Typical of cool, flowing waters in the Rocky • Mountain West and elsewhere are species such as Hannaea arcus, Diatoms vulgare, Cladophora glomerate, Gomphonema sp., Achnanthes lanceolate, Nostoc sp., Hydrurus foetidus, and vario- us species'~Nitzsci~nd NavicuTa whit- w~ ere well represented in the collections. Most o~ these taxa reached abundant numbers sometime during the study period. A general trend was observed in pollution tolerant tax a. Lower stations usually supported more pollution tolerant taxa and at higher relative abundance than did upstream stations. Periphyton species such as Hydrurus foetidus, Gomphonema olivaceum, Nitzschia sp., and Diatoma vulgare are considered to be indicative of stream waters which may have elevated organic concentrations. The general trend is for decrease in species and increase in pollution tolerant forms from upstream to downstream locations. The North Fork of the Gunnison River illustrated the least decrease in species as opposed to the other sampling points. Many of the species observed on the North Fork of the Gunnison River are ubiquitous in distribution (i.e., occur- ring in many different types of habitats under various environmental conditions). Most of the taxa are alkali- philous, indicating alkaline conditions as preferred water quality. Most of the taxa identified are common in the cold, fast flowing streams of the Rocky Mountain West. • Although the periphyton study was qualitative, field observations indicated a definite seasonal cycle of abun- dance. In general, high flows in the spring and early Sumner scour the periphyton growth from the stream sub- strates. The substrates were recolonized during Sumner and early fall, and periphytic algae remained fairly common until winter. During the winter a decline in abundance occurred because the streams were frozen over and many other physical conditions were below optimum for good growth. Scour was highly evident in the North Fork of the Gunnison River. Even though the physical factors respon- sible for the seasonal cycle varied in degree between systems, maximum standing crops of periphytic algae in this stream occurred in late summer and fall, and minimum growths occurred in winter to early Sumner. thic Mac roinvertebrates Although the streams on the Mt. Gunnison No. 1 Mine study area differed widely in physical characteristics (width, depth, rate of flow, etc.), there were many simi- larities in their benthic fauna. One characteristic of all C~ 2.04-70