There are a few extra items you can get here. You're going to need at least 20 Rupees and some Deku Sticks. If you need either, break the jars near the shop, enter the shop and then exit to find the jars have respawned. When you're good to go, run up to the room where King Zora is and light one of your Deku Sticks, then run downstairs and light the unlit torch there; this torch will always remain lit. Light another Deku Stick, then run down and past the shop, lighting the first torch just past it. The second torch is in the water, next to a circle of stones, with the last two torches being behind the waterfall. Lighting all four will reveal a chest in between the last two, containing a Piece of Heart.
For the next item, head back up to King Zora's chambers and take the path to the left, where you'll find a Zora. You can give this Zora 20 Rupees to play the diving mini-game. He'll throw 5 Blue Rupees into the water below, which you must collect by diving off the cliff and going underwater. If you collect all 5 rupees within the time limit, head back up to get the Silver Scale from the Zora who started the mini-game.
Dive back down into the water again and you should see an opening underwater, which leads to Lake Hylia.
