As part of Sidon of Zora main quest in Zelda Tears of the Kingdom, you will have to find and pick up a unique fish, the Ancient Arowana. Ancient Arowana fish is required to restore the Zora Armor which will allow you to swim up waterfalls in Zelda TotK and ultimately reach the Water Temple.
As a reward for finding Ancient Arowana and giving it to Lady Yona, you will be given the first piece of Zora armor and can then move to the other quest objectives.
How to start Sidon of Zora quest in Zelda: TotK
To get the Sidon of Zora quest, you need to head towards Zora’s Domain in Lanayru Great Spring. Head inside the domain and talk to Yona. This will start Sidon of Zora and the first step you need to do for this is to find Ancient Arowana to continue with Restoring the Zora Armor objective.
Where to find the Ancient Arowana fish in Zelda Tears of the Kingdom:
To find the Ancient Arowana fish, you need to head towards the Shatterback Point in Lanaryu Great Spring Region.
Continue down the water stairs and find Gruve on the water pool on the north of the Shatterback Point.
Inside the pool are Ancient Arowana fish. You can either swim towards them or shoot an arrow at them to collect them.
Alternatively, we were also able to find the Ancient Arowana fish on the Great Sky Island. You have to arrive at the waterfall basin located on the west side before the large lake.
There, you can clearly see yellow fish swimming in the water basin. These are the Ancient Arowana fishes. To get them, you can approach them or you can shoot an arrow at them to collect them in your inventory.
You only need one Ancient Arowana to complete this part of the quest. Bring the fish back to Yona at Zora’s Domain and give it to her. As a reward, she will give you the first piece of the Zora Armor. Now you are ready to meet King Dorephan and eventually complete Clues to the Sky.