Physicians, physical therapists, cognitive therapists and others working in rehabiltation for patients with physical injuries, esp. those with brain injuries who may be "starting over" in developing cognitive and physical skills

I once covered a "swimming for non-swimmers" class at my college. Check for something similar around your neck of the woods.

CDC and water-related associations: Red Cross, PADI, American Swimming Association or U.S. Masters Swimming, American Lifeguard Association

Thanks, everyone! Great suggestions.

Try leisure studies researchers -- they can tell you about cultural attitudes towards swimming. Should also explain how it went from something you learned out of necessity to a middle-class kids' activity.