We have measured the 134Cs, 137Cs, 137Cs and 210Pb vertical distributions in a lake sediment core. A value of 0.042 Bq cm-2 has been estimated for the atmospheric 137Cs fallout originating in Chernobyl release on the Alpine area: it represents 15% of the residual 137Cs activity due to nuclear tests. Mixing process and sedimentation rate have been deduced from 134Cs and 210Pb distribution. Distribution of 137Cs has been simulated for slow and rapid mixing processes and for various mixing thicknesses. Comparison with the experimental distribution indicates values of mixing thickness and sedimentation rate in agreement with the previously measured ones. ¿ American Geophysical Union 1988