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populations following the completion of dams has been summarized by Gebhards (1975) and the effects on benthic organisms has been reviewed by Ward (1976). A number of excellent references on streamflows and the ecological requirements of aquatic organisms are provided in Giger (1973), Hooper (1973), Hynes (1970a), Orsborn and Allman (1976), Stalnaker anc Arnette (1976), Tennant (1976), and Wesche (1973). Water Quality Considerations of water quality were historically directed at human health prob- lems and the relationship of water quality to the diversity and abundance of aquatic organisms was used as an index of the po- tential threat to human health. Recentl~ federal laws, such as the Federal Water Pollution Control Act Amendments of 1972 (Public Law 92-500), have become much broader in scope and provide protection to aquatic life as well. Water quality cri- teria have been established from the pub- lished literature (Committee on Water Quali- ty Criteria 1972; McKee and \'lolf 1963) and these criteria are being revised as new information becomes available. Literature reviews are becoming more frequent (Kim et al. 1975) and excellent textbooks such as Warren (1971) help to synthesize the complex problem of water quality. As the human population increases in thE' United States and other parts of the world, more inorganic and organic materials can occur in surface waters. Water has always been important to the development of our country but often there are conflicts that arise from water management since there is competition between the competing uses (Bishop 1971). Varying land uses can great- ly influence the nutrient levels of waters (Omernik 1976). However, the type of use will have some effect. For example, logging practices may result in the buildup of or- ganic materials or sediments in the stream- bed and cause highly turbid waters during runoff (Gibbons and Salo 1973). Depending upon the soil and mineral characteristics of a logged watershed, other water quality parameters will be affected in varying de- grees. Leachates from the bark of trees may be directly toxic to larval and juven- ile fishes that adults may avoid. Mine acid pollution (Spaulding and Ogden 1968) or toxic heavy metals (Tsivoglou et aL 1959) may devastate the aquatic life in a stream. Fish differ from other vertebrates in that they must maintain an osmoregulatory balance of the body tissues despite harsh environmental conditions, particularly water chemistry (Hoar and Randall 1969). The difficulty in monitoring the physiologi- cal condition of wild fish populations was reviewed by Wydoski and Wedeneyer (1976) and clinical methods for assessing the affects of environmental stresses on fish health were summarized by Wedemeyer and Ya- sa take (1977). Changes in water quality NATURAL ~ . . 0-20 em Depth GRAZED I ~ 20-40 em Depth o 20 WATER RETENTION 40 (% at 1 5 a tm. ) Figure 6. Water retention of soils along Rock Creek, !1ontana that are affecred by live- stock grazing compared with natural areas. (Data from Table 3; Marcuson 1977). 65