Many times I was at a public pool, which had a mix of blacks and whites, and none of the blacks knew how to swim. Wade in the shallow end. Yes. Swim, no.
Took a drown-proofing class once where our hands were tied behind our backs and we had to jump into the deep end of the pool. Theory was you could hold your breath long enough for you to float to the top. When the back of your head came to the surface you would lift your head up and back and take another deep breath and back down you went. We were not allowed to kick up off the bottom. Repeat, repeat, repeat. It actually works.
Instructors were standing by to dive in and get you to the top if you were in trouble, just shake your head back and forth as the trouble sign and they were there in a flash.
One black guy in the class. He simply could not float at all. Something to do with your body density/mass being heavier than the water you displace. He gave it a good try but after about 30 seconds under water he started shaking his head right away.