Aerial photographs of transverse shear flows around islands in Rupert Bay, a shallow and turbid estuary in northern Quebec, were studied for the effect of bottom friction. The island wake depends on the stability of the transverse shear layers developed along the two sides of the island. Two basic patterns of wake flows were observed. A vortex street wake was formed when transverse shear was large, as in flows around small islands. On the other hand, for small transverse shear, as in flows around large islands, the shear layers were stabilized by bottom friction and, in that case, a clear water wake of low turbulence and low sediment concentration was observed. Laboratory demonstration of the bottom friction influence on the turbulent wake in shallow water was made using a shallow water table. A similarity solution was obtained for the wake flow in the far-field region, and numerical calculations were made of the recirculating flow in the wake bubble. A wake stability parameter was introduced for wake classification and for correlation of field and laboratory data. In Rupert Bay, vortex street wakes were observed in nine out of 27 events when the wake stability parameter was less than a critical value. The result is consistent with the laboratory and numerical simulations. ¿ American Geophysical Union 1987