<< I actually don't see how you can pass high school gym without knowing how to swim >>
That's very simple, since swimming has nothing whatsoever to do with high school itself, as all high schools have different requirements and different resources. Our school had a broken pool (been broken for about 20 years now) but the other major high school had one. Even so there was NOTHING about swimming in PE. In fact, there was really nothing about physical fitness in PE, it was just a way to get the kids out of their hair for an hour a day I think. Most worthless classes ever conceived of, around here anyway. I've met some people that actually did stuff in PE, but not any where around here.
I can swim, could before the navy, got MUCH better while in the navy. Haven't done it much lately although my apt's do have a couple pools.