Nice idea and a really interesting concept! I can see the potential. It's a bit of a shame that there isn't much to do yet, though. It would have been really cool to have mechanics that prevent the player from walking underwater, forcing them to use a boat to travel between the islands.
But for a game made in just 3 days, it's already a great job. I'm looking forward to seeing a more developed version and testing it again if you decide to continue working on it. (And I really think you should cause you can do it!)