You will require water-proof bombs. Speak to one of the Zoras swimming around the lakebed temple; one of them will offer to sell you such bombs and, if you already have a bomb bag full of another type of bomb, offer to buy any bombs to make space for these new bombs.
Set down a bomb on the cracked area below the lakebed door. This will release a torrent of air. Set down another bomb, which should float up to the door; once it explodes, you're free to enter the water temple.
in the main room
kill the lakebed temple boss or collect enough heart pieces
you need to go to the lakebed temple in lake hylia
his in a room on the ceiling
It's at the bottom of Lake Hylia. You should have gotten the Zora Armor by now. From there, put it on and just go the place marked on your map.
In the sea temple.
If you want to find the BOSS for the Lakebed Temple on Twilight Princess, you have to get the BIG KEY and then go to the room with the giant swiveling staircase, and just jump into the water. The BOSS DOOR is level with the water surface under the swiveling staircase. This BOSS is the coolest one so far. -Caveman1593
In the first temple
Death Mountain
For the first part, use the clawshoot to pull Morpheel's eye out. For the second part, chase after him and use the clawshhot to pull yourself to his eye and attack it.
Beat the first three levels. Forest Temple, Goron Mines, and Lakebed Temple.
It's on the map.