The Quequén Harbour is located in the south-west of Buenos Aires Province, Argentina, and extends to both sides of the last 2 km of the Quequén Grande River estuary. To provide deep water conditions for navigation, the depth is kept by continuous dredging generating an abrupt step with respect to the thalweg bed further upstream and causing particular flows associated with tide and wind. The results of a four-day campaign are used to analyze the local flows around the step after the occurrence of a local wind known as “sudestada”. The velocity profiles obtained reveal longitudinal variations of speed with similar characteristics to those of the waves generated in shallow waters in different time scales. The Fourier analysis of the longitudinal distribution of speed averaged in depth indicates the presence of standing waves of fundamental length and some higher harmonics when they are related to the length of the harbour.