He pointed out that blacks have a heavier/denser skeletal frame so that they don't get injured as much running, etc. However, (now he didn't say that but I came to the conclusion) that would make them heavier in the water. There are very few Olympic swimmers that are black. (This man didn't just focus on blacks, he went into the physical frames of, say, Asians and how they are basically made for gymnastics and diving --- stuff like that.
I found it interesting because he was looking at the differences in the physical bodies of different ethnic groups and how that affected which sports they were good at. Of course, it was immediately called "rascist" and the man became a pariah. Such sillines.
It may simply also be a case that minority parents just don't see this as a priority for their children where, whites do. Maybe the parents just need to be educated in how important it is for the child to be able to swim, even just a little.
Swimming is one sport that seems to be dominated by whitey Northern European types.