Lake Mashu

Lake Mashu sits in a caldera in eastern Akan-Mashu National Park, called Kamui-to ('lake of the gods') in the Ainu language. With no rivers flowing in or out, its water stays remarkably clear, averaging 20 meters of transparency since 2000, producing the deep color known as 'Mashu Blue.' Two observation decks offer different perspectives: Deck No. 1 faces the partially collapsed Mt. Mashu crater across the water, while Deck No. 3 provides the best vantage for the 'unkai' sea of clouds that rolls over the caldera on early summer and autumn mornings.