you actually don't go over the water you have to go around by talking to eddo's assistant he will open a gate then you go through the gate and follow the path good luck :)
Go to cannon island, there should be a cave near the south. go through using bomb flowers to bomb rocks/cracks, bomb rocks blocking a path to the door on the right of the factory, and in there is...
after your first visit to the temple of the ocean king to save linebeck, do what the game is implying you do and then you go in the second time grandpa will walk in and say "grab the hourglass up...
You go to the end of the temple of the ocean king and kill 9 phantoms with the sword (By hitting them in their backs) and beat the final bosses 3 forms.