After surfacing, you should see Navi pointing to something under the water. Dive down to find another Empty Bottle, only this one has something already inside. Head to the shoreline and go up to the two scarecrows. The one on the bottom is named Bonooru and if you take out your Ocarina, you can play any notes you want (must be eight notes) that will be dubbed the Scarecrow's Song. This is completely optional and only lets you get to otherwise unreachable spots later on in the game, with nothing more than non-important items.
Head to the building nearby and if you have a spare Magic Bean, plant it in the soft soil patch behind the building. Release some bugs near the same soil to get a Gold Skulltula to appear. There's another Gold Skulltula on one of the pillars on the small island, but it only appears at night.
Next up is another mini-game, and possibly the biggest one of the game. Swim over to the right side of this area and enter the building on the piece of land that is slightly separated from the main land. This is the Fishing Pond, and as its name suggests, it's a fishing mini-game. Check out the Fishing Minigame section for more details. You want to catch the 10 pound fish, which will get you a Piece of Heart from the man at the counter.
You can now head back to Zora's Domain via the same hole used to get to Lake Hylia.
