The general objectives of this study are (1) to assess the effects of reservoir construction and operation on water quality in the Sun and Teton Rivers and in the proposed project reservoirs, (2) to ascertain what benefits are achieved or lost from changes in water quality, (3) to assess the suitability of the water for proposed water uses, and (4) to determine the need for and value of streamflow regulation for the purpose of water quality control. The necessity of streamflow regulation was studied not only in light of present conditions but also for anticipated future conditions in the study area to the year 2075. The study area includes the Sun River Basin in Lewis and Clark, Teton, and Cascade Counties and the Teton River Basin in Teton and Choteau Counties. (Author)