A numerical model for the transport of suspended particulate matter (SPM) in the Elbe Estuary is presented. The physically based SPM model applies the Lagrangian concept and includes advective as well as diffusive transport, interaction with the bottom sediment in terms of deposition and resuspension of SPM, and sinking of material. Three different SPM concentration peaks, which are caused by different mechanisms, form from an initially homogeneous concentration. One is the generally accepted concept of estuarine circulation, leading to an accumulation through upstream residual currents near the bottom of the mixing region. The remaining two peaks occur in the freshwater region and are therefore attributed to the barotropic velocities. ¿ 1999 American Geophysical Union