This paper demonstrates the effects on local mass transfer of placing a variety of partial obstructions in the form of fences or steps ( arranged in single or multiple configurations) on the walls of a parallel plate electrochemical flow cell. For the wall on which the fence is placed, a plot of the position of mass transfer relative to an obstruction against the Reynolds number for different fence heights shows that, for each fence, the distance to peak position initially increases with the Reynolds number, but tends to decrease al higher Reynolds numbers. For the wall opposite to the fence, a pronounced peak immediately opposite the obstruction, corresponding to a position of maximum velocity, and a second downstream peak, corresponding to a recirculation/reattachment zone, were identified. A correlation of the peak Sherwood number as a function of the Peclet number for all fence heights and also for a backward-facing step was compared with data of other workers. The numerical prediction of flow reattachment to the walls produced excellent agreement with the positions of peak mass transfer for both the fences and the step, but agreed less well in terms of magnitude.