Black sportsmen?

We all know that black spotsmen and women are good, and in a lot of cases , the best in the world at what they do. Whether it's football, golf, cricket, boxing, athletics, or many other sports, there is a black man or woman near or at the top.One sporting discipline is missing though, swimming and water sports in general, why is there no black man or woman at the top or even participating at a high level in that particular field?