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_....___...h..._~~......~_.._ _ .u,... . . J. ...~ stable environments. Water degraded in temperature or chemical composi- tion can displace, or limit growth in fish populations. However, projects providing planned flows can mitigate and potentially enhance fish popula- tions in some environments. Estuaries are also sensitive to alter- ation and reduction of stream flow. Eggs and larvae of some estuarine fishes cannot tolerate high salinity of the marine environment that may re- sult from reduced freshwater flows. In this case, the quantity and seasonal timing of freshwater inputs are partic- ularly critical to these sensitive stages. Productivity of estuarine food orga- nisms partially depends on the al- lochthonous material transported by rivers. Reservoirs may act as nutrient traps thereby reducing estuarine pro- ductivity. Instream flows are a public trust, and stream ecosystems must be protected as irreplaceable resources. Natural stream systems, if properly managed, can provide sport, subsistence, and commercial fisheries at little cost. How- ever, unless stream flows are estab- lished, implemented, and protected, the following impacts can be expected to accelerate: 1. Replacement of unique regional fauna by fishes adapted to the more regulated stream environment. This extirpation will result in more listings of endangered species. Stream fishes currently considered as endangered will continue to disappear in nature. 2. Reductions in localized stream flooding will continue to degrade bot- tomlands and reduce stream produc- tivity, adversely affecting stream fishes. 3. Riparian habitat will continue to be degraded, and degradation will ad- versely affect stream quality. 4. Reductions of stream flows wiJI reduce and degrade stream habitat, increase summer water temperatures, reduce oxygen, and concentrate pol- lutants. 5. Fluctuating flows associated with power generation will reduce stream resources by promoting unstable chan- nels. Such flows will alternately scour, then promote downstream siltation of stream habitats. 6. Loss of spring peak flows below dams will result in perennial armoring of stream bottoms, with downstrea";; effects of wider, shallower channels due to loss of stream power to move sediments. Alteration of natural hy- drographs will result in changed spe- cies composition. May - June 1990 19