The Goznor Shaman can brew you up a concoction which will allow you to breathe underwater, allowing you to reach the Water Temple under Lake Qur, but you must first bring him the necessary ingredients, which are:
- Water Essence x4 - Fish Scales x6 - Pixie Dust x1 - Serpent Crest x1 - Aquamarine x1
These can likely be found in Aeropolis, to the south.
First and foremost, head to Aeropolis, where most of the ingredients are sold.
One Water Essence is sold in the magic shop, and four more by pedlars around Aeropolis. Moreover, some may be dropped by Axolotls as well.
You should have some Fish Scales from Sekils in Sun Temple. If not, you can hunt for some in the various places, like the Soothwood, or buy four from the pedlar in front of armour shop, and another from the pedlar in front of Yalortian Monastery.