Okay, okay, you need an action replay hacking device. Enter in sprint with L+up, then start the game. Go in jolly rogers bay, and see the sign next to the ledges- it should say about slow walking with the touch screen. Anyway, 2 a-presses then sprint!! Press a again as soon as you've passed the wall. When you land in the water slightly beyond the wall (If you've gone too far, see the second bit), swim outside of the wall, until you see the cave from above. Swim down, go through the ceiling, and hey presto, one flooded cave.

My second bit needs moon jump to rectify the mistake and transform jolly rogers bay into dry rogers bay. Moon jump back towards the stage but don't go too high!! Stay below the water line while you getting close as to keep it dry. Then, when you finally get back in the stage, if done correctly, jolly roger bay will be dry as long as you don't cross the water line. And, with this, you can, not surf on, but pick up, that shell in the oyster. Enjoy.