From introduction: This report relates to the first of the above objectives by describing stream quality in the Yampa River basin through 1976, with particular emphasis on conditions from August 1975 through September 1976. The content of this report is, at times, relatively technical. This is intentional. The report is aimed not at planners and decision makers but rather at those persons assigned the task of having to design, implement, and interpret a river basin assessment. The techniques and procedures used to determine ambient stream quality in the Yampa River basin have been presented in detail so that their applicability to other river basins can be determined. For the planner and decision maker, the results presented in this report are summarized in less technical terms in phase-l (Steele and others, 1979) and phase-ll summary reports.