The complex 3D dynamical behavior resulting from the interaction between a plane mixing layer and the wake of a cylinder is investigated using the proper orthogonal decomposition, applied to data from two synchronized 2D PIV systems. An analysis of the correlations shows different length scales in the regions dominated by wake like structures and shear layer type structures. In order to characterize the particular organization in the plane of symmetry, a Galerkin projection from a slice POD is performed. This leads to a low-dimensional dynamical system that allows the analysis of the relationship between the dominant frequencies and leads to a reconstruction of the dominant periodic motion suspected from previous studies Heitz (1999).