The Deep Blue Color Called "Mashu Blue"
Located 11 km from Teshikaga and 12 km from Kawayu Onsen, the surface of Lake Mashu sits 351 m above sea level. With a 20 km shoreline, an area of 19.2 km2, and a maximum depth of 211.4 m, the waters of this crater lake have been called the clearest in the world and it mesmerizes visitors with its ever-changing surface. The lake is surrounded by the crater wall, which is 300-400 m tall and has an average grade of 45 degrees. No other lake in Japan has such an unforgiving shoreline.
The waters of Lake Mashu are not only beautiful, they also have a sense of pureness and innocence. The night sky above is as clear as the lake itself, so the Lake Mashu Stargazing Tour is quite popular with visitors.
Lake Mashu is situated within a national park, but to ensure that this natural splendor is conserved, the area around the lake is additionally designated as a Special Protected Area.
Lake Mashu's water level somehow does not change even though it has no inlets or outlets. It is also referred to as Kiri no Mashuko (loosely translated as "Foggy Lake Mashu") since it is often shrouded in fog, but can suddenly reveal itself in all its mysterious splendor. The water contains almost no contaminants and has a unique deep blue color that is known as "Mashu Blue."