When a high-flow-rate circular jet impinges vertically on a horizontal plane, it flows out radially and then undergoes a distinctive hydraulic jump on the plane because of boundary layer separation induced by hydrostatic back pressure. The jump radius is shown to be 0.37 a Re(1/3)Lambda (similar to1/8),where Lambda = (ga(3)/nu (2)) Re-7/3 is a modified Froude number, Re = (Q/av) is the jet Reynolds number, a is the jet radius, and Q the liquid Row rate, which is favorably compared to experimental data in the limit of small Lambda. When Lambda exceeds 3.0 x 10(-4) at low Row rates, the jump radius decreases below a minimum in the film depth and our experiments detect a different jump mechanism that may be triggered by capillary pressure rather than hydrostatic pressure,