Multiple use management of aquatic systems frequently involves conflicting demands from the various user groups. A 4-year program designed to evaluate large-scale artificial fertilization as a potential management tool for enhancing the forage and game fish populations of Lake Mead, a large Colorado River reservoir, generated considerable attention from both on-lake and downstream water users. An extensive water-quality monitoring program, undertaken as part of the fertilization experiment, demonstrated that the nutrient additions did not produce significant negative impacts on Lake Mead water quality from either a public health (that is, drinking water) or environmental perspective. One set of parameters, for example, hypolimnetic oxygen depletion and the relative abundance of blue-green algae, exhibited no consistent response to the fertilizer. A second group of parameters did respond to fertilizer addition, but changes were both moderate and relatively short-term. Examples in this group include chlorophyll, threshold odor number, and trihalomethane formation potentials.