True story: a friend of mine, Ken, was in Mexico visiting a friend who was convinced this was true, that if you swam after eating you would die. Ken, to show him the ridiculousness of this, swam after eating. The friend literally cried watching him. And wouldn't you know it? That night, Ken got terribly sick with a truly horrible intestinal bug. "Call the doctor," he begged his friend. The friend looked at him. "It won't do any good. You're dying. You swam after eating." Ken did manage to call the dr and survived to tell the tale. We assume there was something IN the water that made him sick.