Lake Mashu摩周湖[ Mashu ko ]

Lake Mashū (摩周湖, Mashū-ko) (Ainu: Kamuy-to) is a endorheic crater lake formed in the caldera of a potentially active volcano. It is located in Akan National Park on the island of Hokkaidō, Japan. The lake has been called the clearest lake in the world.

from Lake_Mashū (Wikipedia) CC BY SA 3.0