Sunken Chest
There’s lots more to do around the Great Bay Coast, but now that you’ve got the Zora Mask, you should briefly return to previous locations for fun and profit. Soar to Milk Road, and then go east into Termina Field. Avoid the item-stealing Takkuri bird as you head for the Termina Field’s west chest, which has sunk to the bottom of a pond. Put on the Zora Mask, dive to the bottom, and open the chest to obtain a Red Rupee.
Heart down Under
Time to quickly get another goodie here in Termina Field. Go west toward the sandy path that leads to the Great Bay Coast. Keep an eye out for a big boulder near the west fence that you recently jumped with Epona. Use the Blast Mask or a bomb to destroy the boulder and uncover a hole.
Drop into the hole to visit a secret underground cavern that’s filled with water, along with dangerous Bio Deku Babas. Use the Hero’s Bow to safely cut the Bio Deku Babas from their lily pads, then aim at the ceiling and notice three beehives. Shoot another arrow, and knock down the hive on the right.
Bio Deku Baba
Damage: 1/2 Heart
These bad plants reside in deep water and often hang down from long stalks attached to the bottoms of lily pads. Like regular Deku Babas, they strike out at Link whenever he approaches, and they’re easy prey for the Hero’s Bow. However, once struck by an arrow, Bio Deku Babas are cut from their lily pads and begin to stalk the sea floor, becoming mobile and even more dangerous. Hit Bio Deku Babas with a second ranged attack for good measure.
The beehive splashes into the water and breaks at the bottom, freeing a Piece of Heart. Put on the Zora Mask, and dive after your prize. Touch the floor, and then press 
+ 
to wipe out the two Bio Deku Babas that you recently cut down from the lily pads. Scoop up the Piece of Heart afterward, and then return to the surface.
Piece of Heart #23
You got a Piece of Heart! Collect four Pieces of Heart to assemble a new Heart Container. Each new container you put together increases the amount of life energy you can have.