Hiking and walking fans should not miss the walk from Zao Onsen to this crater lake on Mount Zao, at an altitude of 1,700m/5,577ft. Its name, Okama, (which literally means "saucepan to cook rice") refers to its circular shape; it is also called the "lake of five colours" because its acidic, transparent waters which are often emerald green, change during the day depending on the season and amount of sunshine. The lake was formed following the eruption of Mount Zao in the 18C.