Thanks for playing, I'm glad you had fun!
Originally, you would start with a sword and unlock swimming and the harpoon by collecting treasures or finding them, but that had to be cut for time.
The water walking "bug" is deliberate, the step is only checked on a 1/4 second interval, so you can abuse that to walk across water. I did it as an homage to the hovering glitch from Zelda: A Link to the Past.
The harpoon area on the right was accidentally made unsolvable when I was "fixing" it (there was no rock to get back, so I added one, blocking off the way to get IN). Everything else should be possible without the bug!
I posted a map of all the treasure locations at the bottom of the page if you're curious.