Lake Mashu

Lake Mashu, located in the eastern part of Hokkaido, a 5-hour drive from Sapporo, is situated within the Akan-Mashu National Park. It is a carter lake that was formed about 7,000 years ago, renowned for its high transparency and the most transparent carter lake in all of Japan. The lake covers an area of 19.2 square kilometers (7.4 square miles), with a maximum depth of 211.4 meters (693.6 feet), and its water has a mysterious deep blue hue. Mists often rise from the surface of the lake, making it difficult to see what it really looks like.

Lake Mashu

The lake is surrounded by cliffs that are 300 to 400 meters (1,000 - 1,300 feet) high, with an average slope of 45 degrees, making it one of the most precipitous lake shores. In the center of the lake is a small island known as Mashu Lake's dimple, which rises only about 30 meters (100 feet) above the lake's surface, actually a very small part of the top of a 240-meter (780-foot) volcano that emerges from the lake's surface. Besides, in order to allow tourists to better appreciate the beautiful scenery of Lake Mashu, three observation decks have been set up around Lake Mashu.

Observatories around Lake Mashu

1. Lake Mashu Observatory No. 1

The Lake Mashu Observatory No. 1, located on the southwest side of Lake Mashu, where you can enjoy a splendid view of Lake Mashu and the surrounding mountains, is the most popular observation deck for viewing Lake Mashu.

Sunrise view of Lake Mashu

2. Lake Mashu Observatory No. 3

Lake Mashu Observatory No. 3, located on the west side of Lake Mashu, is the highest of the three. What makes it attractive is the close-up view of the island in the center of the lake and a completely different perspective of Lake Mashu compared to the Observatory No. 1.

3. Uramashu Observatory

Located on the northeastern side of Lake Mashu, the Uramashu Observatory is characterized by its dense forest, which limits visibility. However, because it is lower in height than the other two observatories, it is notable for being closer to the lake and less affected by fog. Additionally, because this observation deck has few visitors, you can enjoy Lake Mashu in peace.

Note: Uramashu Observatory is only open from April to November.

Best Things to Do in Lake Mashu

1. Admire the Miracle Sea of Clouds

The “Miracle Sea of Clouds” at Lake Mashu is called so because of its high frequency of appearance and magnificence. It usually appears from June to September. The sea of clouds refers to the fog over Lake Mashu, which accumulates mainly during weak winds at night and lasts until early morning. The thickness of the sea of clouds reaches its peak around 2:00 - 5:00 am, and it can be viewed from observatories around Lake Mashu.

2. Hiking

The Lake Mashu Observatory No. 1 is the entrance to the hiking trail, especially in the fall, when hikers come in droves. It is a 7.2-kilometer (4.5-mile) one-way hiking route on the left of which you can see the southern edge of Lake Mashu from the outer rim of the mountain. Along the way, you can enjoy the scenery of the mountain, and climbing to the top of the mountain will give you a breathtaking panoramic view of Lake Mashu below.

3. Stargazing

The Lake Mashu Observatory No. 1 is also a famous stargazing spot, and if the weather conditions permit, thousands of stars can be observed here. The roof of the Lake Mashu Kamuy Terrace at the observatory is open at night, and you can enjoy the starry sky on the provided benches.

How to Get to Lake Mashu

The closest airports to Lake Mashu are Memanbetsu Airport.

→From Memanbetsu Airport, take a bus to Abashiri Station and board a train on the Semmo Main Line to Mashu Station.

→From Mashu Station, take the Mashu Line Bus and it will take you 25 minutes to reach the Lake Mashu Observatory No. 1. This bus only runs once a day, departing at 10:30 in the morning, arriving at the Lake Mashu Observatory No. 1 at 10:55, and returning to Mashu Station at 11:23.

Admission Fee:

Free admission

Recommended Tour Time:

1 - 2 hours

Nearby Attractions

1. Kami no ko ike - A Beautiful Blue Pond

A blue pond near Lake Mashu

After driving from the Uramashu Observatory for 20 minutes, you will arrive at the Kami no ko ike, whose blue waters are crystal clear. It is said that the pond was formed by underground water from Lake Mashu. In the sunlight, the water sparkles with a cobalt blue glow.

2. Mount Iō

The Mount Iō near Lake Mashu

Mount Iō is about a 30-minute drive from the Lake Mashu Observatory No. 1 and is an active volcano. The surface of the rock has over 1,500 volcanic vents that regularly emit sulfur-scented smoke, as if the earth's heart is beating. 

3. Kawayu Onsen

Kawayu Onsen is just a 20-minute drive from the Lake Mashu Observatory No. 1. There are several hot spring hotels here, and the quality of the hot spring water is highly regarded.