The Zoras evolved over the span of a century into the Rito after the events of the Great Flood because of the unnatural water created by the gods, which was uninhabitable to Zora. They live in Dragon Roost Island, specifically within the Rito Aerie, a small cavern to the side of the island mountain.

Why does BotW have Zora and Rito?

In order to stay safe and have a plentiful food source, the Zora would have needed to evolve to survive on land and in turn became the Rito. In Breath of the Wild, the Zora and Rito are seen coexisting together.

Why did the Zora evolve into Rito Reddit?

The Zora evolve into the Rito from exposure to Valoo's scales. This is the only way we've seen this to happen, other methods like natural evolution over time are speculation (not saying it's not possible, just unprecedented). The Rito in WW were starting to naturally have bird qualities.