Lake Mashu is, in Ainu language, "Kamuy-to". Called God's lake, a mysterious place it is.
When on the observation deck you stand, deep blue colored lake water to the extent of as if to be sucked in spreads out, and by the clouds' movement, moment by moment, its expression changes and goes on. This blue is called "Mashu Blue", and in the lake water that boasts first-class transparency even in the world, the sky's blue reflects and enters, and a unique color is born. On wind's not existing days, its blueness even more stands out.

The lake's surroundings, having become a steep wall and being, and to the lake surface descending thing is not possible. Lake Mashu's surroundings are, a National Park's Special Protection Area. The people not letting approach beautiful lake's mystery is, eternity's time having passed through, now still many people attracting does not stop.