In the present paper, organized turbulent motions in an open-channel cavity flow are examined by using wavelet transforms. Experimental data of velocity vectors are obtained by particle image velocimetry (PIV). At first, a multiresolution approximation (MRA) is employed to decompose the PIV velocity data into components of the organized turbulence and the mean flow structures. Then, distributions of an instantaneous Reynolds stress in the organized turbulence are analyzed using a two-dimensional continuous wavelet transform (2D-CWT) in order to detect the coherent structures with their spatial scales and locations. From the results of the wavelet analyses, behaviour of the organized motions along the mixing layer of the open-channel cavity, such as the evolution of the spatial scale and advection velocity, are discussed in different hydraulic conditions.