Lake Mashu (Mashuko)

What to know

Lake Mashu (摩周湖, Mashūko) is a caldera lake in Akan Mashu National Park. It competes for the title of the clearest lake in the world and is often regarded as Japan's most beautiful lake. It is also one of the country's deepest lakes, famous for its strikingly clear blue water, though it is frequently shrouded in thick fog.

Visitors cannot descend to the lake itself, but two observation decks on the caldera rim offer spectacular views. Observation Deck Number 3 is on the western rim and features two viewing platforms with unobstructed vistas of the lake and Mount Mashudake. It has free parking but no other facilities.

A five-minute drive south brings you to Observation Deck Number 1, which has paid parking (500 yen, also valid at nearby Mount Iozan), multiple viewing decks, restrooms, and a large shopping area with a food stall selling Hokkaido specialties. Observation Deck Number 2, once located between decks 1 and 3, is now closed to the public.

For more perspectives, a hiking trail from Observation Deck Number 1 follows the caldera rim about one-third of the way around the lake to the summit of Mount Mashudake, the prominent volcanic peak on the western shore. The trail winds through forest and grassland for roughly seven kilometers and takes 2.5 to 3 hours one way.

Due to very limited public transport, the best way to reach Lake Mashu is by rental car. The observation decks are a little over an hour from Lake Akan and 20–30 minutes from Kawayu.

Infrequent buses run year-round between Mashu Station and Observation Deck Number 1 (20 minutes, 570 yen one way).