Lake St. Clair is dominated by the hydraulic flow associated with the St, Clair River inflow and the Detroit River outflow. This chapter analyses and compares the current measurements made in Lake St. Clair during 1985 with results of hydrodynamic models. To model the circulation by the usual hydrodynamical methods would be very time-consuming in view of the fact that water-quality studies require water movement computations over extended periods of time. Based on theoretical considerations and experiments with a time-dependent hydrodynamic model of Lake St. Clair, it is shown that the currents adjust themselves to the wind within a period of a few hours. The chapter deals with wind-induced variations of the surface level and the associated currents. The empirical model shows that the current directions vary strongly with wind speed due to the associated mixing of the water column.