Lake Mashu is a caldera lake formed by the accumulation of water in a depression created by a huge eruption about 7,000 years ago.
The lake is the second clearest in the world (the first is Lake Baikal in Russia).
The reason for the high transparency is that there are no rivers flowing in or out of the lake, and the water temperature is low throughout the year, making it difficult for organisms to live in the lake, which prevents impurities from forming in the water. In addition, the surface of the lake has a unique and beautiful deep blue color, which is called “Mashu Blue.
Since the song “Mashu Lake in the Fog” became a hit in 1966, Japanese people have an image that Lake Mashu is always covered with fog, however, the surface of the lake isn’t visible for about 20% of the year.
