Introduction to Lake Shikotsu: Lake Shikotsu is a crater lake formed by the eruption of three volcanoes 30,000 years ago. The total length around the lake is 42km, the maximum depth is 360m, and the average water depth is 256m. The lake is clear and has a visibility of 20 meters deep. It is known as the deepest lake in Japan, second only to Lake Tazawa in Akita Prefecture, and is known as the second-deepest "huge water tank" in Japan. The water temperature is very low all year round, but because the lake is 112m below the sea level, it does not freeze even in the severe winter. It is the northernmost ice-free lake in Japan.