During the story quests "Clues to the Sky" and "Sidon of the Zora", I've been told to let Sidon know if I find clues about a land of the sky fish. I found a waterfall coming from a fish-shaped "Floating Scales Island" east of Sidon I assume is the answer. I swam up the waterfall to the island then went back and talked to Sidon, but nothing happened.
How do I let Sidon know I've found the land of the sky fish (Floating Scales Island)?