Great Bay Coast
After Link has been re-united with Epona, you can access a couple of new areas. The first one you should hit is Great Bay Coast. Not only will you get the Zora mask here, but also there are two dungeons that are located here as well as some small quests to do.
Your first task is to get to the Bay. Exit out of West Clock Town and call Epona. Ride down the beach at a full gallop to jump over the barriers and enter Great Bay Coast.
Once you arrive there, you will be in an area with two buildings. The one to the left holds another Spider Dungeon, which you can read about in the Side Quests section. Out in the water is a building on a wooden platform. If you swim out there, you can hit the owl statue to allow you to return to this point via the Song of Soaring.
To get the Zora mask, swim out in the bay until you are about halfway between the building and the beach. You should see an injured Zora floating in the water. Push him to the shore and then play the Song of Healing for him to receive the Zora mask.
Now that you can swim underwater, you can get inside the Pirate Fortress and get the Hookshot as well as some items that are needed to learn the next important song. Before going to pirate bay its advisable to get the rock mask so the pirate will ignore you. Go to the road leading to Ikana Canyon and when you see the circle of stones use the lens of truth a injured soldier will appear. Give him some red potion to receive the mask.