At first, historical bathymetrical maps were digitized and cross-sectional areas and orientations of the different channels were calculated. The most important morphological change in the mouth area was the growth of the Wielingen. This growth is caused by either a changing outflow direction from the basin, or by the preferred channel location as a result of phase differences between tidal water levels and flow velocities, and wave action. The changes in the Wielingen resulted in a decrease in channel area of the Scheur and the Deurloo and in a shift of the northern channels towards the north. The western part of the Oostgat deepened after back-barrier dams were built in the Eastern Scheldt.