Lake Akan and Marimo: Hokkaido's Moss Balls

A quiet lake in eastern Hokkaido where velvety green algae balls roll along the bottom and Ainu culture is part of daily life.

Published October 18, 2026 at 8:50 PM JST | By Tokyo Paul

Quick answer: Lake Akan is a caldera lake in Akan-Mashu National Park in eastern Hokkaido, famous for marimo, round green balls of algae protected as a Special Natural Monument. The lakeside town of Akanko Onsen has hot springs, boat cruises, a marimo exhibition center and an Ainu village. Buses connect it with Kushiro and Memanbetsu airports in roughly two hours.

What marimo are

Marimo are rare, spherical colonies of freshwater green algae. Their scientific name refers to a species that grows in several northern lakes around the world, but in most places the algae form flat mats or loose strands rather than neat balls. Lake Akan is renowned because its conditions encourage the algae to gather into soft, velvety spheres that can reach the size of a baseball or larger. The balls form as gentle currents roll the algae along the lake bed, shaping them over time. They grow very slowly, adding only a small amount of size each year, so a large marimo may be many decades old.

In Japan, marimo hold a special place in popular culture and appear as mascots, souvenirs and aquarium pets. They have been protected as a natural monument for decades, and removing them from the lake is not allowed. In Japan, the name is often written with characters that suggest a ball of water grass, and the creature has long been cherished in folk stories and local identity. Scientists study the lake to understand why the balls form here, and monitoring programs track their numbers and condition. This research is one reason visitors are asked to leave the lake bed untouched.

Seeing marimo at Lake Akan

To see wild marimo up close, visitors take a sightseeing boat from Akanko Onsen to Churui Island on the lake. A small marimo exhibition center on the island displays living specimens in tanks, with explanations of their growth and the efforts to protect them. Boats offer commentary and views of the lakeshore and surrounding forested mountains.

Note that you will not wade into the lake to collect marimo, and the natural balls are generally not visible from the surface. The exhibit provides the best view. Boat schedules depend on season and weather, so check the official page for current departures. Early in the day, the lake is calm, and the views of the forested peaks are especially clear.

The Marimo Festival

Every October, the community holds a Marimo Festival, a ceremony that honors the algae and the lake. It is a friendly event with a mix of Ainu traditions and local activities, often including a boat ceremony. In the ritual, marimo are returned to the lake, expressing respect for the water and a hope for its continued health.

Because the festival dates vary slightly each year, check with the local tourism association. Visiting during this time lets you see the community's pride in its natural treasure. Autumn leaves in the surrounding forest add to the scenery, and the weather is cool and crisp. Book accommodation in advance if you plan to attend.

Akanko Onsen and the Ainu village

Akanko Onsen is a compact hot spring town on the south shore of the lake. Its main street has souvenir shops, small restaurants and hotels, many with baths overlooking the water. The town also has a collection of carved wooden items and crafts, reflecting the influence of Ainu culture.

The Ainu are the indigenous people of Hokkaido, and a village in the town presents their traditions through crafts, shops and performances. A theater hosts dance and music, including pieces recognized as important cultural heritage, and visitors can watch with explanations in Japanese and sometimes in other languages. Please treat the shops and performances with respect, as they are living expressions of a culture, and ask before photographing individuals.

Activities across the seasons

In summer, the lake area is comfortable and cool, suitable for kayaking, hiking and camping at designated sites. Trails lead to viewpoints and volcanic features around the national park, with forests of conifers and broadleaf trees. Insects can be active, so bring repellent. In winter, the lake freezes, and activities include ice fishing for smelt and walking on the frozen surface where permitted.

Snow festivals and evening fireworks may be held, subject to conditions. Dress very warmly, because temperatures in eastern Hokkaido can drop well below freezing. Always follow local guidance about ice safety, and avoid venturing onto the ice unless an organized program is in place.

Food around the lake

Local restaurants serve Hokkaido dishes such as grilled fish, soup curry and jingisukan, a style of grilled lamb. Wakasagi, small smelt caught in the lake, may appear on menus as tempura or grilled. Dairy products from the region, including milk and soft serve ice cream, are common treats. Some shops make marimo-themed sweets and souvenirs.

Cakes, cookies and candies shaped like green balls are popular gifts. Hotels often serve elaborate dinners, so ask about meal plans when booking. Prices and menus vary, so look at displayed options when choosing a place to eat. A warm bowl of noodles on a cool day is always welcome.

Getting to Lake Akan and respecting the marimo

The lake is in the eastern part of Hokkaido, away from the main rail lines. Buses run from Kushiro Airport and Kushiro Station to Akanko Onsen in roughly two hours, depending on the route. Buses also connect from Memanbetsu Airport, near Abashiri, and from Kitami. Timetables vary by season, so check them before traveling. Renting a car is a good option for exploring the broader region, which includes Lake Mashu and Lake Kussharo, but winter driving needs experience. If you rely on buses, plan an overnight stay, as services can be limited.

Taxis and tour buses are also available for sightseeing in the national park. Lake Akan also fits well into a loop of eastern Hokkaido lakes and volcanic scenery. Lake Mashu is known for its steep crater walls and deep blue color, while Lake Kussharo has hot-spring shores and a large island. Some visitors build a two or three day route through all three, which works best by car or with a guided tour, since public transit between them is sparse. Visitors are asked to respect the natural environment.

Do not take marimo or other living things from the lake, and avoid disturbing shorelines. Stick to marked trails, and carry your trash out. In the town, follow local rules for parking and quiet hours. Marimo souvenirs sold in shops are typically cultivated rather than taken from the protected lake. If you buy one, keep it in clean, cool water, change the water regularly and keep it out of direct sunlight. Rolling it gently from time to time helps it hold its shape. Many owners treat them as long-lived companions, with a little care.

Frequently Asked Questions

What is a marimo?

A marimo is a ball-shaped colony of green freshwater algae that grows slowly in certain lakes. At Lake Akan, the algae form soft, velvety spheres that are protected as a Special Natural Monument. They can be seen in exhibits and at the lake's Churui Island.

Can you take a marimo home from Lake Akan?

You must not remove marimo from the lake, as they are protected. Shops sell cultivated marimo as souvenirs. If you buy one, keep it in cool, clean water, away from direct sunlight, and change the water regularly. Looking at the living specimens in the exhibition center on Churui Island is the best way to appreciate them.

How do you get to Lake Akan?

Buses connect Lake Akan with Kushiro Airport, Kushiro Station and Memanbetsu Airport, with rides taking roughly two hours depending on the route. Check the seasonal timetables before you travel, and consider an overnight stay. Renting a car is helpful for exploring nearby lakes, though winter driving needs experience.

Keep Exploring

More guides from Tokyo Paul: Hokkaido Prefecture Travel Guide, Lake Toya: Hokkaido's Caldera Lake and Kushiro Wetland: Japan's Largest Marsh.