Drop into the water and swim along the right wall to a ledge. Then equip your Iron Boots and drop down to the bottom. go in the hallway with the torches on both side of it and go in there to meet Ruto. Walk to the center of the room after she leaves and take off your iron boots to float up. Play Zelda's Lullaby in front of the Triforce symbol and the water level will lower. Go through the door to get your dungeon map. Drop down and you'll be in a room with two unlit torches and a lit one. Light the torches by shooting arrows through the lit torch or use Din's Fire. Go in there and kill the clam guys. To kill them ,Z target the clam and hold down your hookshot button to aim at it, then walk up to it until it opens it's mouth and then release the button to fire the hookshot. 

Now go back into the main room.Follow the left wall, skip the next tunnel and go on to the tunnel after that with the block in front of it. Push the block all the way and it will drop down. Jump down and go down the passageway then up the other side. Now hit the switch (the thing that looks like a diamond) and jump onto the geyser that shoots up then jump over to the other side. If you fall down there's a hookshot target you can use to get back up. Now you'll be in a room with a big whirlpool. Equip your Iron boots to sink down. 

Go stand on the piping under the water across from the stone head. Aim your hookshot to hit the switch in it's mouth, then turn and fire the hookshot at the hookshot target inside the underwater passage. Go down the passage and float up and grab the key, then hit the switch that's in there to reopen the gate and use your Iron Boots to walk back out. Take off the boots and float back out of the whirlpool and make your way back to the main room. You'll need to use the hookshot to get out of the hole at the end of the tunnel. Stand on the block you dropped down then look up and you'll see a hookshot target you can use.You should have 2 keys now. 

Go to the tower in the middle of the main room and find the locked door and go through it. Use your hookshot to go up to the ledge above you then play Zelda's Lullaby in front of the Triforce symbol to raise the water level. Now put on your Iron Boots and drop back down. Underneath where the block was is now a hole. Drop down and follow this corridor and you'll end up in a room with a switch. Hit it with your hookshot from a distance and back away as a bunch of bad guys drop down from the ceiling. Here's a battle tip for you. use Z-targeting the spiked urchin and hit it with your hookshot to kill it and it won't even be able to attack you. If it does come at you, block it with your shield and it will turn back into a rock. 

Walk around Z targeting all the urchins and kill them and you'll be left with two clams. Kill them using the hookshot strategy you used before. Once they are all defeated a grate on the other side of the room will open in the ceiling. Float up there to get another key. Go back to the tower room and go through the upper door. Walk around until you see a tunnel with two pots in front of it and go in there. Follow the hall, use your hookshot to get over the spikes, then use your hookshot again on the ceiling to get up in the room. Go stand next to the treasure chest and shoot an arrow at the switch. Then get the compass. Go back out to the main room. Jump in the water, put on your boots, and sink to the bottom.Walk into the room where you saw Ruto and float up. Blow up the crack in the wall to get your third key. Now go back into the main room, unequip your boots and swim left across the wall. 

Enter the first locked door you see. Go stand on the water spout and then shoot an arrow at the switch and it will push you up to the next room. Go through the door and you're at the high water level Triforce mark. Play Zelda' Lullaby to raise the water level. Now drop into the water and swim left to a locked door and go through it. Hop down two platforms and this platform will move. When it's at it's lowest point jump to the non-moving platform to your right. Now use your hookshot on the hookshot pads onhe moving platforms to make your way up to the top of the waterfall and go through the locked door. Now your in the water level puzzle room. Use your hookshot on the switch in the middle of the room to raise the water, then hookshot over to the statue nearest you. 

Now shoot the switch again with the hookshot and the water will lower. Walk to the back corner of this platform and look to your right. Use the hookshot on the hookshot target on the wall to get over to the next platform. Climb over the statue head and walk to the edge and shoot the switch again to raise the water. Now hookshot to the next statue and hit the switch to lower the water. Now stand on top of the statue's head and shoot the switch the last time to be taken up to the next level. Kill the annoying spider things and kill the Like-Like with arrows then use the hookshot target in the ceiling to get over the spikes. Go through the door and you'll find yourself at a shallow lake with a tree in the middle and a pillar on the opposite side. Walk across it and walk up to the pillar on the other side. You can't enter the door, so turn around and you'll see a little black shadow of yourself.

Stand on the island in the center of the lake and make sure he stands on it too. For some reason, if he's standing on the island he won't attack nearly as well. Use Din's Fire if you want but I used my hammer. If he blocks your hammer then just hit him with your sword then quickly pull out your hammer and quikly give him a good whack. Go through the door to get a hookshot upgrade called a Longshot. Now look behind the chest and therewill be a block. Use the Song of Time and drop down the hole. You'll be at the mouth of a river. Swim down river and when you start coming close to a whirlpool, use your Iron Boots to walk past it. Make your way to a small platform on the left side of the river. There will be a whirlpool that you will have to walk as far up the edge as possible and un0equip your boot and hit the B-button as fast as you can. 

Use an arrow to shoot the gold eye across from you and a grate will open with a treasure box behind it. Use your hookshot on the treasure box to get across, avoiding the last 2 whirlpools, and open the box to get a key. Go down the hallway and you're back at that whirlpool you got a key from earlier. Now make your way back to the main room and with your Iron Boots on go through the tunnel with the torches on either side where you met Ruto, and float up to the water level changing switch. Play Zelda's Lullaby to change the water level, then drop down and go back into the main room. Go into the tower and play Zelda's Lullaby there to raise the water to the middle level. Exit the door and go around the tower to the back. There's a tunnel here with a grate and a gold eye below the entry. 

Shoot the gold eye with an arrow then quickly use your Hookshot on the Hookshot target at the end of the hall. Follow the passage until you hit a movable block. Push it forward out of your way, turn left and get the key. Now go back the other way and use your hookshot to fly up the hole in the ceiling and go down the hall to drop down back into the main room again. Sink down to the bottom and go into the passage to the right of the passage leading to the room where you met Ruto. Float up the other side. Use your hookshot to get over the spikes and go through the locked door. In this room kill as many of those spider things as you can first then use your Iron Boots to walk through the middle of the water, avoiding the whirlpools and the boulder. Float up and out on the other side and go through the door. Drop to the nearest ledge on your right and blow open the crack in the wall. 

Don't go through it yet. Instead, swim across to the left platform and blow open the discolored bricks. Go through this one and push that block that's in there all the way forward. Now loop back around to the first hole and go in there and pull the block as far as you can. Loop back around once again and push it the rest of the way onto the underwater switch. This will raise the water level. Float up with it and go through the door (not the one you came through, the other one. It's got steps in front of it). Now in this room step on the floor switch and quickly cross the gap by hopping on the water spouts then go through the door. You don't have to jump on the third geyser, you can make the jump from the second to the door to save time. In here avoid the boulder and head right (upstream) then use your boots to sink into the deep water. 

Walk along the passage, float up the other side and go through the locked door. Get the Boss key from the treasure chest. Now go back outside, go down stream and you're back in that room with all the spider things and the vortex's. Go back through the door you first came in and make your way back to the main room again. Once there float up and go through the door with the red block floating in front of it and raise the water to the highest level. Now look for one of those dragon head statues with a hookshot target on it. Use the hookshot to get over there and go through the door behind it. Go up the ramp while trying to avoid those moving spike things (this is a lot harder than it sounds. Try going up the right side when the first spike thing is moving to the left and about halfway over and keep running straight up) and go through the boss door. Jump onto one of the platforms and you'll get a warning about the water. Now you'll meet Morpha.