Iwana bōzu are enormous iwana (char, Salvelinus leucomaenis), a kind of river fish, that have turned into yōkai. They walk upright on two legs like humans and dress in Buddhist priest robes. They are found by mountain streams where people fish for iwana and other river fish. Iwana live in rivers and streams high up in the mountains. Iwana which survive for many years and grow to an enormous size become iwana bōzu. They learn to transform into human shape, leave their rivers, and even speak.