As I thought about my reply there was one more thing I would like to say. Pointing your flippers at what you would want to avoid would work if your back wasn't pointed directly upstream. Then you would simply hit more slowly. Safety on a river involves knowing what the water you are sitting in as opposed to what the average of the the waters between the banks are doing. There can be dramatic differences. There are times when the water is actually flowing upstream as in elevator eddies. I have seen two currents folow off of shelves into each other and act like techtonic plates. Reflex waves coming off of rocks generally have a current at the top of the wave going in the down stream direction; if the wave is 2-3 feet one can be pushed sideways 4-5 feet; great fun; generally a Class Three or better experience. The idea is to look ahead and pick a safe path that gets you to where the fish are. There are numerous white water organizations that will be glad to teach this stuff; its fun and you will get to places that you can't walk to.