The purpose of this study was to develop and apply a procedure for measuring the effects of water quality on recreation benefits. A random sample of 141 households visiting Rocky Mountain National Park were interviewed during the summer of 1973. A substantial portion of the park is located in the South Platte River Basin, Colorado. Perception of water quality was based on color photos depicting six levels of water quality in the River Basin. Willingness to pay questions were designed to measure consumer surplus which is the area under the demand curve for outdoor recreation. The demand curve shifts with changes in the level of water quality. The stepwise multiple regression procedure was utilized to develop linear demand functions. Standard statistical tests of significance were shown. Although the willingness to pay questions were hypothetical, they were designed to be as realistic as possible. Willingness to pay was measured in terms of a recreation entrance fee, the value of waterfront recreation property and travel time. These are familiar methods of paying for outdoor recreation resources. The valuation procedure used in this study has been successfully applied to other natural resource and public good problems. Park visitors were willing to pay an average of $5.42 more in entrance fees, 165 percent more for waterfront recreation property and devote 89 percent more travel tine to gain natural water quality. The statistical relationship between benefits and perception of water quality as measured on a 100-point scale from worst to best conceivable showed that park visitors were willing to pay $0.06 more daily recreation fee to avoid each one unit decrease in water quality. They were willing to travel 0.9 percent more and to pay 1.9 percent more for waterfront recreation property. The annual benefits of water quality are shown for the park, and non-resident benefits are calculated for the river basin and the state. Present value of perpetual benefit streams are developed for the three areas. The study shows the statistical relationship between benefits from water quality and patterns of participation in outdoor recreation activities, attitudes, and other socioeconomic variables. Policy implications are developed for governmental agencies in outdoor recreation and water quality management.