Swimming culture is one that has primarily developed in rural (due to ponds and natural water structures) and suburban (due to more readily available community pools) areas. In these areas it is expected that parents know how to swim and thus can help teach their children and, particularly in the suburban areas, there are more readily available classes to formally teach children to swim. This in turn leads to another generation of people who can swim and thus will teach their children to do so.
Urban areas, where space is more of a premium, have considerably less access to community pools and the pools that are available typically have higher fees for usage. As a result pools are both less available and more costly, making it harder for people growing up in urban areas to regularly swim, particularly people in the lower-classes. As such people growing up in urban areas are less likely to be competent swimmers than ones in suburban or rural areas. This has a generational impact as you have parents that can't swim well who aren't able to teach their children or don't consider swimming to even be all that important. Black people disproportionately live in urban areas and thus are disproportionately impacted by this. This is further compounded by the fact that until the 60's public pools were often segregated thus making learning to swim even more difficult for people of color. Which means that parents were less likely know how to swim, which in turn meant they weren't able to teach their kids, who could not teach their kids.
This in no way is to imply that black people cannot swim, but as a result of multiple historical and economic factors make it less likely when compared to your average white individual.
could have mistaken this for a stormfront post ---