Velocity and density sections across Knight Inlet, British Columbia, demonstrate that lateral recirculations are a first-order feature of the flow in the lee of the sill. The flow over this sill has been used as a typical example of two-dimensional hydraulics, with a lower layer that thins and accelerates as it moves downstream below an almost stagnant layer that widens downstream, creating a distinctive wedge shape. However, we find that rather than being stagnant, the velocity in this wedge-shaped layer is actually quite large, consisting of a swiftly recirculating dipole vortex during flood tide and a monopole vortex during ebb tide, though we may have missed the matching half of a dipole with our sampling during ebb. The recirculations during flood tide carry an amount of water equal to 25% of the tidal flux, while the monopole during ebb tide carries 20% of the tidal flux. These recirculations bias along-channel estimates of volume flux, especially in the middle wedge-shaped layer, and demonstrate that accurate volume fluxes in the lee wave are only possible if three-dimensional surveys are made. Our three-dimensional survey shows that there is a net isopycnal convergence of water in the middle layer at a rate adequate to close the volume budget of the flow without recourse to diapycnal fluxes. We also calculate the strength of the vorticity in the recirculations observed during flood tide and attribute their formation to boundary layer separation. ¿ 2001 American Geophysical Union