The nonlinear Schr¿dinger equation derived by Liu and Tsay (1984) is used to investigate the forward scattering of the second-order Stokes waves by a depth discontinuity. It is shown that, due to nonlinearity, stem waves develop along a line caustic. The structure of the present stem waves is similar to that found by Yue and Mei (1980) along the wall of a thin wedge.