Marimo of Lake Akan: Japan’s Rare Green Treasures
Deep within the pristine wilderness of Hokkaido’s Akan-Mashu National Park lies a natural phenomenon that borders on the magical. Lake Akan, a caldera lake known for its crystal-clear waters, is home to the Marimo (Aegagropila linnaei)—velvety green spheres of algae that have captivated scientists and storytellers alike. While these moss balls exist in a few other places in the world, the Marimo of Lake Akan are unique in their size, shape, and cultural significance. Designated as a Special Natural Monument of Japan, these green treasures offer a fascinating glimpse into the intersection of biology, conservation, and Ainu folklore.
The Origins: A Biological Miracle
Despite their resemblance to moss, Marimo are actually a species of filamentous green algae. The name “Marimo” was coined by Japanese botanist Tatsunosuke Kawakami in 1898, combining mari (bouncy ball) and mo (aquatic plant).
While the algae filaments grow in many lakes across the Northern Hemisphere, they rarely form the perfect, velvet-like spheres found in Lake Akan. The unique geography of the lake creates the perfect storm—quite literally—for their formation. The shallow basin combined with specific wind patterns generates gentle, rhythmic currents that roll the algae along the lakebed. This constant motion ensures that all sides of the clump receive sunlight for photosynthesis, allowing them to grow radially into spheres. Some specimens in Lake Akan have reached diameters of over 30 centimeters (12 inches), making them the largest in the world. It is a delicate balance of nature; if the currents are too strong, the balls break apart, and if they are too weak, the algae settle and rot.
The Legend: A Tragic Ainu Romance
Before scientists analyzed the currents of Lake Akan, the indigenous Ainu people of Hokkaido had their own explanation for the existence of these mysterious spheres. The folklore surrounding Marimo is as beautiful as it is tragic, echoing the timeless themes of forbidden love.
According to the legend, the daughter of a local Ainu chieftain fell deeply in love with a commoner. Their union was strictly forbidden by the constraints of their social hierarchy. Desperate to be together but unable to defy her father’s decree, the lovers fled to the shores of Lake Akan. Realizing they could never live peacefully in the human world, their spirits transformed into Marimo, allowing them to live together eternally at the bottom of the lake, rolling side-by-side in the currents.
This story has imbued the Marimo with a romantic symbolism in Japan. Today, they are often viewed as charms for enduring love and relationship longevity, a tangible representation of two souls intertwined against the odds.
Modern Culture and Conservation
In modern Japan, the Marimo has become an icon of Hokkaido tourism, but its popularity once threatened its existence. In the early 20th century, poaching and environmental changes caused a drastic decline in the Marimo population. In response, the local community and the government launched rigorous conservation efforts.
Central to these efforts is the Marimo Matsuri (Marimo Festival), held annually in early October. The festival is a solemn and celebratory event led by Ainu elders. It involves a ritual where Marimo are respectfully returned to the lake, symbolizing the preservation of nature and the honoring of the spirits. It is a powerful fusion of environmental awareness and indigenous cultural heritage.
Travelers will see Marimo merchandise everywhere in the town of Akankohan, from keychains to “pet” Marimo sold in jars. Note that the souvenirs sold in shops are artificially rolled from common algae filaments to satisfy tourists, protecting the natural, wild-formed Marimo in the lake from being harvested.
Traveler’s Tips: Seeing the Marimo
Because the wild Marimo grow on the lakebed in protected zones, you cannot simply walk to the shore and spot them. To see the massive, natural spheres, you must take a specific route:
- Marimo Exhibition Center: Located on Churui Island in the middle of Lake Akan, this center is the only place to view the giant, natural Marimo up close in large tanks. The center explains the science of their formation and the conservation history.
- Sightseeing Cruise: Access to Churui Island is exclusively via the Lake Akan Sightseeing Cruise boats. The ride takes approximately 85 minutes round-trip and offers stunning views of Mount Oakan and Mount Meakan.
- Best Time to Visit: While the lake is accessible year-round, the boat cruises operate from May to November. Winter offers a different experience, with the lake freezing over and hosting ice festivals, but the Marimo are best viewed during the warmer months.
Sources & Further Reading
For those interested in the deep cultural history of Japan and its indigenous peoples, the following context is helpful:
- Ainu Oral Traditions (Yukar): Unlike the Yamato Japanese history recorded in texts, Ainu history was passed down orally. The Marimo legend is part of this rich oral tapestry.
- Historical Context: While mainland Japanese mythology is heavily documented in the Kojiki (712 AD) and Nihon Shoki (720 AD), these texts focus on the Shinto pantheon and the Imperial lineage of Honshu, Kyushu, and Shikoku. They do not cover the flora or folklore of Hokkaido (then known as Ezo). Understanding Marimo requires looking beyond these imperial texts to the distinct cultural heritage of the Ainu people.
- Scientific Reference: The Biology of the Marimo by various botanical researchers provides insight into the ecological fragility of Aegagropila linnaei.