Originally posted by: Project86
It looks to be very cleverly edited. In some shots he appears to be steping on something, and in some of the other shots (the angle looking down at his own feet, as if filmed from his own little camera) he is obviously suspended via cables and just making a walking motion with his feet.
My idea is that he has some type of clear plastic columns placed every few feet, and that's what he is walking on. That is also why he is able to drop his shoe: he isn't on a complete platform or anything. That would also explain why they can swim around him. We don't have a good enough angle to know if that girl swam exactly under him, but even that could be facilitated by utilizing a platform shaped like an upside down L (if that makes sense). The "audience" is all in on it. Then they also use a crane or something similar, which is off camera, and suspend him for some of the shots. Some good editing, and you're done.
That being said, this was still a cool trick.