You'll have to use some blue fire to melt some red ice in your way in this corridor.  Open the ice door and you'll face an ice wolf.  Kill it and receive the Iron Boots.  Sheik will come and teach you the Serenade of Water.  Use your new Iron Boots to sink into the water behind the treasure chest and walk to the end of the passage.  Take the boots off once you emerge from the water.  You're now back in the first room.  Before leaving the ice cavern, go back to the small round room where you got the heart container piece and the compass (East of the helicopter blade room) and fill two bottles with fire.  Then go back out the way you came in.  Leave Zora's fountain and use a blue fire on the frozen King Zora.  Talk to him and he'll give you the Zora Tunic, which keeps you from drowning.  Go down and use your other blue fire on the doorway to the Zora Store.  Now play your Serenade of Water and you'll warp to Lake Hylia.  Run forward and jump into the water in front of you.  Make sure you're wearing Zora's Tunic and then turn around and equip the Iron Boots.  Use your hookshot to hit the blue diamond above the doorway and it will open.  Go inside and you're now in the Water Temple so take off those Iron Boots.

Water Temple:

Drop into the water and swim along the right wall to a ledge.  Then equip your Iron Boots and drop down to the bottom.  Find the tunnel with the torches on either 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 that's there and the water level will lower.  Go through the door that's there 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.  Z target a 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. Kill them this way because in a bit you're going to have no choice but to kill clam guys with your 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 forward and it will drop down.  Jump down and go down the passageway then up the other side.  Now hit the shock 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 crystal shock 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 shock 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.