A numerical circulation and transport model is used to simulate currents and trajectories in Lake St. Clair. Results from the model are compared to three different types of measurements, namely (1) mean currents from an array of fixed current meters, (2) currents measured from a ship during seven synoptic surveys of the lake, and (3) trajectories of satellite-tracked drifting buoys during four different experiments. The model is then used to predict the effects of storms on the residence time of water entering the lake from eight tributaries and the probable horizontal distribution in the lake of water from a particular tributary. Results show that although the average residence time of the lake is about 9 days, actual residence times range from less than 2 days to over 30 days depending on wind conditions. The calculated distribution patterns of water from various tributaries coincide closely with observed distributions of some water quality parameters and biota. ¿ American Geophysical Union 1989