Well, here you are again. This time, take the southeast tunnel at the bottom of the Main Chamber (the one with the single green pipe running into it) to reach Room 15.
Room 15: Beneath Waterwheel Room 1
You’re now exploring the room that’s directly below the first Waterwheel Room (Room 2). Surface and swim onto the green pipe that rises up from the water. As soon as you find your feet on the pipe, face the center of the room, and use the Hookshot to burst a bubble that surrounds a Stray Fairy. Draw in the little fellow with the Great Fairy’s Mask.
Traverse the green pipe to reach a spinner. Turn it to complete the water flow and fire up a nearby pump. Now you can reach the Boss Door.
Before using the water geyser to reach the Boss Door, put on the Zora Mask, and dive back into the water. Sink to the bottom, and spot another Stray Fairy in a bubble in the northwest tunnel. Don’t enter the tunnel, or you’ll be sucked back to the Main Chamber. Instead, throw Zora Link’s fins to break the bubble, then return to the green pipe and put on the Great Fairy’s Mask to draw in the final Stray Fairy. (It’ll take a few moments to reach you.)
All right, time to battle the boss. Cross the green pipe again, and then leap onto the water geyser that you started. Let the geyser boost you up, and then leap to the ledge with the Boss Door. Open the Boss Door, and drop down the large hole in the room beyond to advance to the temple’s final trial.