The orthogonality relation of the internal wave equation has been derived and has been included in normalizing the particular modes. Under the assumption that observed currents in western Lake Constance all result from basin-scale internal waves, they can be decomposed into contributions of the particular modes. In all cases of a response to a wind stress, at first the velocity profiles indicate a quite pure first-mode wave. After strong winds, a second-mode wave contributes remarkably and consistently to the velocity profile later during the response. During the zero transition of the first mode, the observed velocity profile can be attributed mainly to a second-mode wave. ¿ 2000 American Geophysical Union