An integral simulation model has been developed for understanding and simulating the process of a density current and the transport of spilled chemicals in a stratified reservoir. The model is capable of describing flow behavior and mixing mechanisms in different flow regimes (plunging flow, underflow, and interflow). It computes flow rate, velocity, flow thickness, mixing parameterized by entrainment and dilution, depths of plunging, separation and intrusion, and time of travel. The model was applied to the Shasta Reservoir in northern California during the July 1991 Sacramento River chemical spill. The simulations were used to assist in the emergency response, confirm remediation measures, and guide data collection. Spill data that were available after the emergency response are used to conduct a postaudit of the model results. Predicted flow parameters are presented and compared with observed interflow intrusion depth, travel time, and measured concentrations of spilled chemicals. In the reservoir, temperature difference between incoming river flow and ambient lake water played a dominant role during the processes of flow plunging, separation, and intrusion. With the integral approach, the gross flow behavior can be adequately described and information useful in the analysis of contaminated flow in a reservoir after a spill is provided.