# Lake Mashu

> A caldera lake 212 m deep, walled in by cliffs up to 350 m high, that you look down on from observatories on the rim; there is no way down to the water. Summer fog often hides it, and the road past the free No. 3 Observatory closes in winter.

- Prefecture: Hokkaido
- Type: Attraction
- Address: Teshikaga, Hokkaido, Japan
- Hours note: The observatories have no gate. The Mashuko Kamui Terrace building at the No. 1 Observatory opens 8:30 to 17:00 with irregular closures and shuts over the New Year; it can close or shorten hours in bad weather.
- Official site: https://www.masyuko.or.jp/enjoy/mashu/

The water sits 351 m above sea level inside a caldera wall that rises another 150 to 350 m, and the rim is as close as you get: the shore is a cliff, the lake is a specially protected part of Akan-Mashu National Park, and no path leads down. What you see from the top is very deep blue, 212 m at the deepest, and in 1931 a transparency of 41.6 m was measured here. The small island in the middle is Kamuishu. Most people stop at the No. 1 Observatory, where the Mashuko Kamui Terrace building has a rooftop deck, a shop and the only toilets. Cars pay 500 yen to park there from May 1 to October 31, and the ticket also covers Mount Io the same day. The No. 3 Observatory, a few kilometers north toward Kawayu Onsen, is free, quieter and has no facilities. The lake is known for fog, which is mostly a summer thing; low cloud tends to lift around midday, so a gray morning is not always a lost day. In winter the road from the Kawayu side, including the No. 3 Observatory, closes from early November to mid-April, but No. 1 can still be reached from Teshikaga town.

## FAQ

### How much does it cost to visit Lake Mashu?

The observatories are free. Parking at the No. 1 Observatory costs 500 yen for a car and 200 yen for a motorcycle from May 1 to October 31, and the same ticket covers the Mount Io car park that day. From November to April it is free. Parking at the No. 3 Observatory is always free.

### Can I walk down to the shore of Lake Mashu?

No. The shoreline is steep cliff and the lake is a specially protected area of the national park, so visitors cannot go down to the water. You see it from the observatories on the rim.

### Will fog hide Lake Mashu?

Often in summer, much less in spring, autumn and winter. In summer the low cloud tends to lift around midday, so it can be worth waiting or coming back. The tourism association runs a live camera you can check before driving up.

### Can I visit Lake Mashu in winter?

Yes, at the No. 1 Observatory, which you reach from Teshikaga town, and parking there is free in winter. The road from the Kawayu Onsen side, past the No. 3 Observatory, is closed from early November to mid-April, and the Ura-Mashu Observatory is also reached only from about April to November.

---
Source: [Lake Mashu — Japan Voyage](https://travel.japanvoyage.jp/travel_destinations/lake-mashu)
Last updated: 2026-10-10