An Acoustic Doppler Velocimeter (ADV) system, with digital signal processing has been used to measure the longitudinal, transverse, and vertical velocity components in three‐dimensional, fully developed open‐channel flow with transversely placed Piano Key Weir (PKW). Simple experiments were conducted to deduce the influence of boundaries on noise occurrence. Both the longitudinal boundary (PKW) and vertical boundary (channel bed) affect noise. Magnitude of noise has been found to be increasing near both the boundaries. Consequences of noise on the first- and second-order velocity parameters have also been estimated. Results show that there is existence of higher correlation between noise and second-order velocity (turbulence) than first-order velocity. After the noise removal from the data-sets, the reduction in the magnitude for the second-order velocity is found up to 80%. Magnitude of reduction is also dependent on the distance from the hydraulic structure. Analyses of data-sets in the horizontal plane indicate presence of noise (i.e. higher uncertainty) below the relative depth 0.3. Where, relative depth is defined as the ratio of point depth of measurement to total flow depth. © 2018, © 2018 Indian Society for Hydraulics.