A reservoir located on the Limmat River down stream from Zürich has been investigated in order to determine the history of sediment contamination since 1930 - 1933, when the dam was built, and to evaluate risk for man and the environment. Levels of contamination by heavy metals and nutrients are low at the beginning, but increase rapidly. High levels are registered from about 1960 to 1975. Recent surface sediments have low levels again. PCB and PAH concentrations are very high at the base ofthe sediments, but decrease rapidly upward. The main source of contamination is up stream, but local sources are identified as well. The main risks for man and environment are linked to the uptake of contaminated sediment or surface water by organisms and to groundwater infiltration; further investigations are currently conducted.