Lake Mashu (First Observatory)
摩周湖第一展望台
A caldera lake once ranked first in the world for clarity. Its deep blue waters are known as “Mashu Blue,” and it is often shrouded in thick fog, earning it the nickname “Foggy Lake Mashu.”
Lake Mashu is a caldera lake formed about 7,000 years ago. No rivers flow into or out of it. Measurements in 1931 recorded a transparency of 41.6 metres, and the lake takes on a deep “Mashu Blue” colour. In the centre of the lake is a small island called Kamuishu Island. The steep crater walls surround the lake, and visitors can only look down from the observation decks. The First Observatory has a rest house called Lake Mashu Kamuy Terrace, and parking is charged. The Third Observatory on the north side is free and offers a wider view. In summer, fog often rolls in, so seeing the full panorama takes luck. In winter, the road to the First Observatory is open, but the Third Observatory is closed. The site is about 20 minutes’ drive from Kawayu Onsen.
Opening hours
All day (third observation deck closed in winter)
Nearby sights
- Mount Io (Atosanupuri)
- Kaminoko Pond
- Kawayu Onsen
- 900 Grassland
- Tawadaira
- Sunayu, Lake Kussharo
- Wakoto Peninsula
- Bihoro Pass