Also, why did they move to Death Mountain? Jabun, their original guardian diety, resides in Greatfish Isle. Comparing the maps of OoT and WW, it appears that Greatfish Isle is above the Gerudo Valley.
The most sense I can make of that is if the entire Zora race, along with Jabu-Jabu, migrated through the passage to Lake Hylia, then upstream a bit, where Din created Greatfish Isle and Farore transformed them into land creatures. But then I have no idea why some of them moved to Dragon Roost.
Or perhaps only some migrated through Lake Hylia and the rest climbed Death Mountain (which neighbors Zora's Domain). That would mean the inhabitants of Greatfish Isle were the human forms of the Zora, and those of Dragon Roost were the ones to whom Valoo gave wings.
But then that raises the question of Valoo... Is he Volvagia? Why is he good now? Why is he supporting the Rito and not the Gorons? Why did the Gorons leave?
When did the zora's move to death mountain? Last time I recall i see them in the domain every game. There may be one or two who travel across the map but they are always in water or near it.