The tidal interaction between two constant depth oceans joined by a rectangular strait of length d, width 2a and constant depth h was analyzed. The strait is narrow in the sense that the scale of the ocean tide in the absence of the strait is much greater than the width of the straight. The following results were obtained. (i) Under the mild restriction that the strait is narrow enough, sea level tidal constants change linearly from one end to the other. If the tides in each ocean differ, steep sea level gradients occur in the strait. These gradients tend to be much steeper than those in the ocean near the strait. (ii) The steep sea level gradients in the strait drive strong along-strait currents which are uniform in the middle part of the strait but change considerably within 0.4a of the ends. (iii) Because of end effects, strong gradients in sea level can occur across the strait even when the width of the strait is much smaller than the strait barotropic radius of deformation. (iv) When the tid... Abstract The tidal interaction between two constant depth oceans joined by a rectangular strait of length d, width 2a and constant depth h was analyzed. The strait is narrow in the sense that the scale of the ocean tide in the absence of the strait is much greater than the width of the straight. The following results were obtained. (i) Under the mild restriction that the strait is narrow enough, sea level tidal constants change linearly from one end to the other. If the tides in each ocean differ, steep sea level gradients occur in the strait. These gradients tend to be much steeper than those in the ocean near the strait. (ii) The steep sea level gradients in the strait drive strong along-strait currents which are uniform in the middle part of the strait but change considerably within 0.4a of the ends. (iii) Because of end effects, strong gradients in sea level can occur across the strait even when the width of the strait is much smaller than the strait barotropic radius of deformation. (iv) When the tid...