Swimming against the current in Japan has never been a good idea, even if you are armed to the teeth with logic and common sense.
Two types of people go to swimming pools -- the serious types who swim lots of laps back and forth across the pool, and the splashers. Whereas the former group swims in straight, predictable lines, the latter group doesn't care where they go as long as they're having fun.
In the world of aquatics, they're a twain that should never, ever, meet.