Jonsau Shrine is in the Lanayru Wetlands on the southern part of Mercay Island.
Shrine Location
Jonsau Shrine is at 1744, 0017, 0025, in the Lanayru Wetlands. It is on the south end of Mercay Island, the northern island of the wetlands.
Deep Force
Use Ultrahand to put the yellow orb underwater, beneath the glowing switch on the ceiling. Put the orb as far down as it will go, then let go. It will bounce up and hit the glowing switch, opening the bars. Go through.
In the next area, use Ultrahand to take the treasure chest out of the water. It contains a Mighty Construct Bow.
Defeat the Soldier Construct in this area, then go to the next area, where there is a brightly-colored slab in the water. Rotate the slab to be vertical instead of horizontal, then hold it under the water beneath the glowing switch on the ceiling. Put it as far down as possible, then let go, and it will bounce up and hit the switch, opening the bars. Go through.
In this area, there is another floating orb, and there is a stone platform above. There is also a piece of wood on the platform above. Put the orb underwater beneath the piece of wood, push it down as far as it will go, and then let go. If you positioned it correctly, the orb will bounce up and knock the piece of wood away. This will allow the platform on the rail to slide down.
Now attach the orb to the bottom of the platform on the rail, put the orb underwater as far as it will go, and let go. The platform will slide up and then down, and will keep bouncing. Use Recall on the platform and wait until you can safely get in. The orb may get detached in the process, but once you are in the rail platform, you can deactivate Recall, and the orb will bounce the platform back up even if it got detached. The platform will launch you up to where you can glide to the end of the shrine. Check on the dragon ring to get a Light of Blessing and complete the shrine.