ABSTRACT: This study assesses the impact of Glen Canyon Dam releases on rafting (white-water boating and day-use rafters) and angling recreationists in Glen Canyon and Grand Canyon National Park using attribute and contingent valuation surveys. Several sources of information were utilized in this study: knowledgeable people (fishing quides, rafting guides, resource managers, and GCES researchers), seven formal surveys (including attribute surveys), and contingent valuation survey to quantify, in dollars, the effects of dam releases on the recreational exoerience. The goal of the study was to assess the impact of alternative annual flow release patterns for Glen Canyon Dam on recreationists in the aggregate. Flow regimes combining high constant flows in the summer months with moderate or low flows during the remainder of the year would be likely to produce the largest recreational benefits. Extreme high or low flows will adversely affect all river recreation, with flows below approximately 5,000 cubic feet per second and above 35,000 cubic feet oer second to both boaters and anglers.