A method for dating pollution by means of ¹³⁷Cs fallout from nuclear explosions into the sediment has been tested in 3 lakes of western Switzerland. The method involves determining the sedimentation rate in grams of dry sediment per surface unit per year and was applied to 6 large diameter cores. Two of them were dated precisely, one with a lesser precision and 3 with minimal or maximal dates because of very high or very low sedimentation rates. Pollution was estimated by the concentrations in the sediments of 2 to 7 trace metals and of 1 or 2 nutrients. The results indicate that sediment enrichment in heavy metals began before the 1930's, slightly increased until 1972 and has been decreasing since then. Nutrient enrichement of the sediment started around 1900 and kept growing steadily until the present time.