Jabu-Jabu's Belly
Use the Slingshot and shoot at the upper tooth, then open the door at the back. Follow the path (ignore the lift), open the next door and you will meet Princess Ruto. Follow her into the hole, then talk to her twice. Carry her (tough luck!), open the door behind you and follow the path. Jump into the water, throw Ruto to the other side, then stand on the switch. The water level will rise and you can now reach Ruto and carry her again. Keep going until the next door and put the princess down. Use the Slingshot on the tooth behind you, then take Ruto and open the door. There you have to take the lift, still with Ruto, and once you've reached the top, jump, go right and open the door. You're back in the room filled with holes, go through the room while avoiding them and open the door in front of you.
As soon as you can, go right and jump on the switch with Ruto on your shoulders. Open the door, put Ruto down and get rid of all the Stingers with your Slingshot when they're flying around. Take the Boomerang from the chest, then pick up Ruto again, get out and go straight ahead to the other switch. Place Ruto on it and get in. Attack the red tentacle with the Boomerang to get the Map, then get out and pick up Ruto. Then, take the first path on the left, get in and break all the bubbles with the Boomerang within the time limit to be rewarded with the Compass. Pick up the princess, get out, go back towards the room where you found the Boomerang, but turn left just before you reach it. Get in, get rid of the blue tentacle the same way you did with the red one, and get out with Ruto. Next, turn right twice, open the door and get rid of the third (green) tentacle. Get out and go back to the room filled with holes, still with Ruto. You must now drop through the hole behind the one in front of you on the right (with Ruto).
Get rid of the two Gold Skulltulas (now you can always retrieve the tokens with the Boomerang). Open the door behind you, then throw Ruto on the platform as she asks you to do. After she finds the Zora's spiritual stone, get close to the platform to meet...
Bigocto
To defeat Bigocto, hit it with the Boomerang to get it stunned. Then as soon as it starts spinning, hit it once again with the Boomerang, and if it shows you its back, hit it quickly with your sword. Repeat these actions several times to defeat it, then jump on the platform and open the next door.
Throw the Boomerang at the first block, jump on it, do the same with the second one, then open the door. Jump on the platform in front of you and you will reach the second room of the dungeon. Grab a crate, drop it on the switch east on the map and open the door. Get down on the right and climb the vines to reach the platform. In order to hit the tooth behind the transparent wall, get close to the edge, use the Z lock and throw the Boomerang so it flies around the transparent wall. Get down from the other side, get rid of the Gold Skulltula and open the boss door.
Barinade
Always keep moving to avoid the electric beams, use the Z lock to aim and shoot the Boomerang at his tentacles. Don't get too close to his body at first. When all the tentacles came off, attack his centre still using the Boomerang. When his belly turns blue, quickly get closer and slash his protecting spheres around him with your sword. When all the spheres are destroyed, keep hitting him with the Boomerang and you will finally be able to hit his body with your sword. Break some pots if you need small hearts. At last, pick up the Heart Container and get into the light where the Zora princess is eagerly waiting for you.
Princess Ruto entrusts you with the Zora's Sapphire, the third spiritual stone.