I don't understand how one CANNOT know how to swim. It's so self explanatory as is learning to walk. I always get puzzled when I hear people complain that they don't know how to swim and are afraid of drowning ... Ummm... could you just TRY to learn? Honestly, it's not hard. Move your arms and legs and you'll get the hang of it.
I mean, they teaching infants how to semi-swim and backfloat now. If they can do it, so can adults.