Since you are on a river you can have a pursuit race with a difference. You need three marks, with the start in the middle (perhaps two actual marks forming a gate) and an upstream mark and a downstream mark. You start at your time, but you can go choose to go upstream or downstream first. You need to round both the upstream and downstream mark and then finish. Boats are finishing from both directions, in theory at the same time. You choose your route based on traffic, potential changes in the winds.