Lake Mashu is a caldera lake located in Hokkaido, Japan. It is known for its stunning blue color and is often shrouded in mist, giving it a mystical appearance. The lake is situated within Mashu National Park and is one of the clearest lakes in the world, with visibility reaching depths of over 20 meters. The lake has a diameter of about 3.5 kilometers and is surrounded by steep cliffs. It is a popular destination for tourists and nature enthusiasts, offering scenic views and opportunities for hiking. Fishing is not allowed in the lake to preserve its pristine environment.