Lake Hylia
Ocarina of Time Walkthrough

Essentially as soon as you've gotten out of the Ice Cavern you can head directly to the next temple. Here are two things you should do.

Zora's Fountain: Heart Piece
Zora's Fountain: Zora Tunic

Next use your new Ocarina tune to warp you to Lake Hylia. Once there, jump down the ledge and find the pool of water. Then put on your Iron Boots and head in. Look for the ecrystal above the door and hit it with your hookshot.

Welcome to the Water Temple.