Tributyltin (TBT) measurements in a food web in the freshwater Lake Westeinder are used to calibrate an integrated fate and bioaccumulation model with special attention given to exposure pathways. The Dutch ban on antifouling paints containing TBT is simulated with a load reduction scenario. By integrating Monte-Carlo sampling with a calibration procedure, probability distributions of TBT concentrations in the food web are matched to the measured variation in TBT concentrations. Subsequently, these distributions are used for a dynamic risk analysis of TBT accumulation in water, sediment, and the food web in the whole lake and a typical marina. Model predictions indicate a fast decrease of concentrations in water, suspended matter, and the zebra mussel Dreissena polymorpha. TBT concentrations in sediment, chironomids, amphipods, and benthivorous fish are predicted to decrease at a much slower rate. Simulations indicate that TBT in the sediment contributes significantly to uptake of TBT by several species. ...