A coastal risk assessment system simulates the basic physical mechanisms underlying contaminant transport in Tampa Bay. This risk assessment system, comprised of a three-dimensional numerical circulation model coupled to a Lagrangian particle tracking model, simulates the transport and dispersion of a toxic dinoflagellate bloom. Instantaneous velocity output from the circulation model drives the movement of particles, each representing a fraction of a K. brevis bloom, within the model grid cells. Hindcast simulations of the spatial distribution of the K. brevis bloom are presented and compared with water sample concentrations collected during the peak of the bloom. Probability calculations, herein called transport quotients, allow for rapid analysis of bay-wide K. brevis transport showing locations most likely to be impacted by the contaminant. Maps constructed from the transport quotients provide managers with a bay-wide snapshot of areas in Tampa Bay most at risk during a hazardous bloom event.