Three sediment cores taken at positions in Lake Constance strongly influenced by the river Rhine and one core taken at a position less influenced by this most important tributary were investigated with respect to the depth distribution of Cesium radionuclides in order to follow up transport processes of contaminated clay particles from the catchment system into the lake. In the depth distributions of Cs-137 well resolved maxima from the Chernobyl fallout and from the nuclear weapons testing fallout were found. Additionally, the high-water event of 1987 is reflected by the depth distributions of Cs-137 at the positions influenced by the river Rhine. The total inventories of Cs-137 activity from the Chernobyl fallout and the nuclear weapon testing fallout are higher compared to the input across the water surface at the positions influenced by the river Rhine, indicating the importance of fluvial input.