Results for hindcast simulations are presented for the transient concentration distributions in Long Island Sound for the pesticides malathion, resmethrin and sumithrin for the period August 1, 1999 through October 19, 1999. The high resolution of the simulations provide information concerning the detailed spatial patterns in time varying concentration distributions that are dependent on the distribution of pesticide loadings around the perimeter of the basin. Plume concentrations attenuate very rapidly with distance from the coast to below 0.001 μg/L; high concentrations are detected only in confined coastal embayments and regions immediately adjacent to the coast. The decay rates used in the simulations have a strong influence on the concentration fields. Concentrations in plumes for pesticides dispersing into the western Sound from the East River also attenuate rapidly with distance from the East River.