Mountain Creek Lake is a reservoir in north Texas 8 miles southwest of Dallas, Texas where historical contamination by polychlorinated biphenyl compounds (PCBs) and other organic contaminants has been reported. There was a need to reassess concentrations of contaminates of organic and inorganic compounds in the reservoir. In cooperation with the City of Dallas, the U.S. Geological Survey (USGS) sampled Mountain Creek Lake and two downstream stream sites over two sampling events. The study area consisted of seven sites on Mountain Creek Lake, one site on the Trinity River, and one site on Mountain Creek. Water-column and bed-sediment samples were collected at each site in June and August of 2019. Water-quality field properties (water temperature, dissolved-oxygen concentration, pH, specific conductance, and turbidity) were measured in the field at each sampling site by using a Xylem YSI EXO2 sonde. Water-column samples were collected by using a peristaltic pump to collect composite water samples that were analyzed for 32 major and trace elements, 6 nutrients, 68 volatile organic compounds (VOCs), alkalinity, dissolved solids (DS), and turbidity. Bed-sediment samples were collected by using a gravity corer for lake sites and grab samples for stream sites. Bed-sediment samples were analyzed for 50 major and trace elements, 17 polycyclic aromatic hydrocarbons (PAHs), 9 PCBs, and 66 VOCs. The USGS National Water Quality Laboratory in Denver, Colorado analyzed water samples for major and trace elements, nutrients, alkalinity, dissolved solids, and turbidity. RTI Laboratories in Detroit, Michigan analyzed water samples for VOCs. Bed-sediment samples were analyzed by RTI Laboratories for PAHs, PCBs, and VOCs. AGAT Laboratories analyzed bed-sediment samples for major and trace elements. This Data Release documents the results of the water and bed-sediment sample analyses.