The Amsterdam rowing course 'The Bosbaan ' does not meet the requirements for international championships. The major concern is that under certain wind conditions, there is an unfairness between the racing lanes of the course, which is called lane difference. Lane differences in rowing contests are caused by inequalities in wind velocities, flow velocities, and wave heights between the lanes. The international rowing federation, the FISA has proposed a widening of the course to 118 meters with 8 in stead of 6 lanes. They assume that this widening will decrease the lane differences. Objective of this study was to verify that assumption, and to propose additional measures to reduce the lane differences. The flow in the Bosbaan was computed with the 3-dimensional shallow-water solver DELFT3D-FLOW. The wind velocities above the course were implemented as surface boundary conditions. The influence of the computed flow velocities on the lane differences (arrival times of boats on the different lanes) is compared with the direct influence of wind on the basis of estimations of air- and water resistance forces. The trees around the Bosbaan cause differences in wind velocity above the course. In addition, this inspace-varying wind field induces a water circulation, with different flow velocities in different lanes. The differences in wave height between the lanes are of minor importance. The differences in wind- and flow velocity are maximal for the two outer lanes: lane 1 and lane 6, and increase with increasing wind speed. These wind- and flow velocity differences result in differences in travel times between the lanes. Which of the two influences prevails, depends mainly on the direction of the wind: for adverse wind, the direct influence of wind on the rowers dominates, while for assisting wind, the larger part is caused by the differences in flow velocity. The proposed widening in northern direction will yield somewhat higher wind- and flow velocities than nowadays. However, there will be an area with relatively lower flow velocity differences. For all wind directions, this area is at the north side of the course, and covers approximately 4 lanes. Compared with the existing situation, the lane differences increase for the lanes 3 to 8, but decrease with approximately 20% for the lanes 1 to 6. However, even with this improvement lane differences remain. Further widening is expected to increase the area with relatively lower lane differences and therefore decrease the lane differences between the lanes. Additional measures to reduce the lane differences can be subdivided into measures to control the wind and measures to control the flow. The first category measures (not examined in this study) are most effective since they remove the cause. The best way to do that is an indoor facility. The second category measures just intend to influence the flow velocity differences. From exploration of likely measures, two realistic possibilities for further investigation arose: (i) lateral fences, slowing down the flow, and (ii) deepening of specific areas of the course, directing the flow.