The wake effect of the probe on the measurement volume to validate the measurements provided by acoustic Doppler velocimeter (ADV), was investigated. A computational fluid dynamics (CFD) model was used to simulate an open channel flow where the model was validated. The measurements were performed using particle image velocimetry technique (PIV) producing two dimensional velocity fields around the acoustic probe measurement volume with and without the presence of the probe. The results show that the wake effect of the ADV may modify the flow field producing erroneous readings of the mean flow velocities and turbulent quantities.