Turbulent structures along a mixing layer in an open-channel flow over a concavebed are analyzed using wavelet transforms. Experimental data of the velocity are obtained by a particle image velocimetry (PIV). At first, we evaluate the accuracy of the PIV velocity data by employing a multiresolutional analysis (MRA). The result of MRA shows that the instantaneous Reynolds stress is an appropriate signal for the coherent structure detection. Then, the distributions of the instantaneous Reynolds stress are analyzed using a two-dimensional continuous wavelet transform (2D-CWT). The spatial scales and locations of the coherent structures are detected from the maximal values of the wavelet coefficients. The characteristics of the organized motions along the mixing layer, such as an evolution of spatial scale, advection velocity, and occurrence interval, are clearly extracted in terms of the location and the time.