In October 1966, the U.S. Geological Survey began a reconnaissance study of water quality in Flaming Gorge Reservoir. The purpose of this study was to determine the load of dissolved ions in the reservoir, the changes in chemical quality of the water as a result of initial leaching and subsequent storage, and the effect of the reservoir on the effluent waters. The construction of Flaming Gorge Dam began in 1957, and the reservoir began storing water in November 1962. This report tabulates the chemical-quality data which were collected during the study (1966-68) and summarizes some of the data available prior to closure of the reservoir. An interpretive report will be prepared at a later date. Three sets of data were collected from the reservoir during the study. The sampling locations are shown in figure 1 and the data are listed in tables 1 and 3. At each site in the reservoir, samples were collected at various depths from the surface to the bottom, using a self-closing messenger-actuated sampler. For sites 1-6, the sampling verticals were at the deepest part of the reservoir cross section. For sites 7-12, in the upper reaches of the reservoir, sampling verticals were at three points in the cross section. Samples for complete chemical analysis were collected from sites 1-6 at both the beginning (October 1966) and the end (September 1968) of the data-collection phase of the study. The variation in dissolved ions with depth for these two sets of data are summarized in figure 2. Samples for partial analysis were collected from sites 1 and 6-13 in September 1967, and the partial analyses are included in table 1.