Elastic wave decomposition, aiming at separating the converted modes from the P waves, is applied to high-resolution OBC data acquired in the River Danube, Hungary. The decomposition relies on accurate knowledge of the water-bottom elastic parameters and on a perfect sensor calibration and coupling. The available decomposition schemes require an adaptation to account for the shallow water depth in the survey area. In the presented method, the medium parameters are obtained from the inversion of the Scholte waves dispersion curves and the coupling filter was determined from the data. The coupling filter accounts for the imperfections in the geophone coupling and was corrected for by minimizing the contribution of the pressure and vertical component to the upgoing S-wave potential at near offsets. This criterion implies that these two components contain no converted energy at these offsets. The estimated coupling filter is applied to the geophone data used as an input to the decomposition scheme. The decomposed S-wave potential showed an improvement in the visibility of some converted modes, mainly at later arrivals.