Lake Mashu (摩周湖, Mashūko) is a caldera lake in Akan Mashu National Park. It vies for the position of "clearest lake in the world", and is considered by many to be Japan's most beautiful lake. Lake Mashu is also one of the country's deepest lakes and although it is usually appreciated for its clear blue water, it is also famously and frequently blanketed in heavy fog.
Visitors are not allowed to go down to the lake, however there are two observation decks positioned around the rim of the caldera from where you can enjoy views. Observation Deck Number 3 lies along the western rim of the caldera and consists of two decks with unobstructed views onto the lake and Mount Mashudake. Besides free parking, there are no facilities provided.
Due to very poor public transportation, the recommended way to visit Lake Mashu is by rental car. The observation decks overlooking the lake can be reached in a little bit over an hour from Lake Akan or in 20-30 minutes from Kawayu.
