After the continue barrel, head down and left. Go up past 3 starfish. At the top use Enguarde's A-charge to the right (to cross an opening before the water level drops).

After the first DK barrel floating in the water go right then up, then use Enguarde's "A"-charge to open a door where the wall is marked with a lone banana.

At the [G] head down and left, drop into the first vertical shaft and swim through the right-hand wall.