A thing that should not be resides deep within the Great Bay Temple’s watery depths. It’s the gargantuan masked fish, Gyorg!
Gyorg is a challenging boss with powerful attacks, so prepare for a tough battle. Fortunately, your initial battle strategy is very straightforward. Gyorg swims about the surrounding water, perhaps considering how to best devour you. The boss is a bit too fast to track with 
-Targeting, so aim manually and shoot it with arrows (any kind, even regular arrows). Gyorg’s head is covered in a hard protective shell, so aim for the monster’s exposed body instead.
After you shoot Gyorg with an arrow or two, the monster flips over, revealing a giant eyeball. That’s its weak spot! Lock on, and pepper the eyeball with arrows to score damage.
Damaging Gyorg angers it, and the monster soon begins to ram your platform’s underwater supports. Don’t worry: this doesn’t harm you. However, Gyorg also periodically emerges from the water, lands on your platform, and then darts forward to ram you. The fiend’s face is protected, so simply roll away to avoid being damaged by its charge.
Keep stunning and damaging Gyorg with arrows until the monster finally manages to shatter your platform’s base. The battle changes at this point, as you’re dunked into the water. Put on the Zora Mask, and keep away from Gyorg; the monster can suck you in and chew you up if you get too close. Hold 
+ 
to swim at top speed and escape Gyorg’s pull whenever necessary.
To stun Gyorg during this stage of the battle, you must trick it into gobbling up one of the many spiky mines that are chained to the arena’s floor. This is somewhat random and takes a bit of practice. Keep close to a mine, and wait for Gyorg to inhale. If the mine is close enough to Gyorg, it will be pulled toward it but kept in place by its chain. Strike the chain to free the mine, then fight against Gyorg’s pull as you wait for the monster to inhale the mine.
Those mines give Gyorg serious indigestion. Each time it eats one, the resulting explosion stuns Gyorg, causing its vulnerable eyeball to pop out. Now’s your chance! Get close and lock on to the eye, then unleash a swift series of Zora Link’s fin attacks. Stun Gyorg with another mine after it recovers, and keep battering its eyeball until the monster is no more.