The transport of solute in rivers and estuaries can be described by a linear convective diffusion equation. Therefore, the principle of linear superposition can be applied to the dispersion data obtained from a short-term prototype tracer test in order to simulate the concentration buildup of a soluble waste resulting from its long-term release. The assumptions are that both tracer and waste decay according to the first-order reaction rates and that the flow is repetitive with a certain period, which may range from a multiple of tidal cycle for an estuary to an infinitesimal time for a steady river flow. Equations are derived to relate observed tracer concentrations to simulated waste concentrations. Examples of field application are presented. It is concluded that this simulation method is quite feasible for a quick and direct pollution assessment under certain conditions.