From the Ancient Zora Waterworks, you create a path to Wellspring Island.
How to Reach Wellspring Island
As part of the quest Sidon of the Zora, you can reach Wellspring Island by using the glowing object in the Ancient Zora Waterworks to create a waterfall. Swim up this waterfall using the Zora Armor to reach Wellspring Island.
Explore the Island
On this island, you will jump higher and fall more slowly.
Go northwest from where you entered the Island, and use Splash Fruit to wash away the sludge on the bridge, as well as the sludge on the treasure chest on the other side of the bridge.
There are floating bubbles of water in this area that you can jump into and swim through or float in.
After you open the treasure chest, go northwest and talk to Sidon. Then go to the nearby device that is tilted at an angle, and stand in front of it. Don't move when the water bubble comes out of it. You should automatically be pulled into the bubble and you will float to the top of it. Stay in this bubble and it will take you to the platform above. You can dash forward to exit the bubble, or just wait for it to pop.
You can optionally go along the area that goes east, where you will find a couple of treasure chests. Then go back to the west side and ride the bubble back up.
Then you can float up in the water bubbles from the floating platforms to reach an area to the northeast. Defeat the Constructs here, then go to the southeast side of this platform and use Ultrahand to take the hydrant. Use it to wash away the sludge, then go down the stairs that you find near the pool of clean water, to find a treasure chest.
Go up the stairs, then go northwest. There is a treasure chest covered with sludge on top of a column, which you can wash away using a Hydrant from the southeast part of this area. Then go to the northwest end of this area and use the Hydrant to wash away the sludge on the platform across from you. This reveals a waterfall.
Equip the Zora Armor and swim up the waterfall (or just glide to the top of the waterfall platform) and you will see several waterfalls in this area. You can also see a shrine to the northwest. Glide to the waterfalls and swim up them to reach Igoshon Shrine.
If you go northwest from the shrine, you will find a Device Dispenser.
From the shrine, go southwest up the nearby stairs, to an area where you find a number of Wings. There is an angled stone at the southwest side of this platform, and if you hit the glowing switch, the stone will pull back, then launch forward. Place a Wing in front of this angled stone, then stand on it and hit the glowing switch to launch the Wing. It will land on the island to the southwest.
Go southwest and up the stairs in the wall. Defeat the Construct, then go south to where there is a waterfall nearby. Equip the Zora Armor and swim up the waterfall. Glide west to the next waterfall, and make your way to the platform to the northwest. Open the chest there to find an old map.
Then make your way to the platform to the southeast, where there are three waterfalls. Defeat the Constructs there, and open the chest that unlocks.
Jump south to the next platform, then use Recall a large water bubble when it is close enough for you to enter. Get in the bubble and it will take you to the south platform.
Go to the east side of this platform and attach two of the flat stone slabs to make a square. Place them against the east wall so that they form a ramp for the floating bubbles. When a bubble hits this ramp, it will be launched upward, so get into one and let it take you upward, then glide to the east platform.
Take a wheeled cart and attach a Wing to the top of it, then attach three fans to the back of the Wing. Place the Wing at the base of the ramp that points northwest, and hit it to activate it. It will take you to the platform where you will find Sidon.
Talk to Sidon and he will join you. Go northwest and defeat the Construct, and there will be a cutscene. Then go northwest and approach Sidon and there will be another cutscene.
Equip the Zora Armor and swim up the waterfall that Sidon went up. Glide forward to enter the Water Temple.