The growth of the Las Vegas Metropolitan area may eventually lead to increased wastewater discharges into the Boulder Basin of Lake Mead on the border of Arizona and Nevada. This growth has led various agencies to accelerate studying the water quality in Boulder Basin and its surroundings. Flow Science, acting under agreement with Black & Veatch, used ELCOM (Estuary and Lake COmputer Model) to model the water quality within Boulder Basin. ELCOM and CAEDYM are three-dimensional finite-difference codes developed at the University of Western Australia. They were used to simulate three-dimensional transport and the interactions of flow, physics, biology, and chemistry in the reservoir.The study indicated that the hydrodynamic flow patterns within Boulder Basin are mainly driven by the Colorado River inflow, the Hoover Dam outflow, and meteorological parameters. However, the water quality of Boulder Basin is also affected by the load of nutrients from the Las Vegas Wash, which carries the treated wastewater effluents from municipal wastewater treatment plants, surface runoff, and groundwater discharges into the basin. This project is still ongoing.