Zora's Domain

Do: Find lake hylia
Get: Silver scale, piece of heart
Meet: Zoras, king zora

From the entrance, go forward and run down and then back up again (it's the way the path is). Then, when you are as far as you can go, go left to find the royal chamber (where king zora is). Speak with him to hear his dilemma with Princess Ruto, she's gone. You will be abel to help with that, but not right now. Go left to find a zora on top of another waterfall. Talk to him, and play his diving game for 20 rupees. After you say yes, he will throw the rupees down the waterfall. Dive down and collect the rupees before time runs out. Once you collect them all he will tell you, and you should get back up there as soon as possible. After you get back up, he will give you the silver scale, which allows you to dive 3 more meters: 6.

If you're a person like I am, and want to get heart pieces alot then read this section, if you aren't, well, skip it.
Get up to the royal chamber and light a deku stick, quickly run down and light the torch below. Then fastly run down to the left and light those two torches then run over to the rocks and light that one. Then stay by the side so you can keep standing, and light the torches behind the waterfall. This will make a chest appear, holding a piece of heart. (You have to keep the same stick out the whole time or the torces will go out and you'll have to do everything all over again.

Now, to get to lake. Go in the deep water, and scour it for a square hole in the wall underwater. Use the new abilities to dive deeper to go through that hole. On the other side is Lake Hylia.