Marimo is emblematic of Lake Akan. Countless souvenir shops and sightseeing attractions line along the streets of Akanko Onsen Town that borrow the word "marimo" in their names. However, there is little known about this creature.
What's marimo like?
Marimo is a species of filamentous green algae which grows through photosynthesis in the fresh water.
They can be seen on the rocks and shells or drifting in the water. The distinctive feature of marimo in Lake Akan is that each algae get together to form a large spherical shape with the power of wind and wave.
Amazingly large over 15 cm. in diameter
However, Lake Akan is not the only place where marimo can be seen. As of 2002, they are found in 17 places in Japan as well as over 50 locations in the cool climate zones of the northern hemisphere. Why they are nevertheless not so familiar to us?
Most of marimo in other places are so tiny or look like messy and not having a good ball shape which only be observed in two places, Lake Akan and Lake Mývatn, Iceland. It is said that marimo in Lake Mývatn are in danger of extinction, which might send Lake Akan would be the last place where a colony of large spherical marimo is witnessed.
But, why marimo can grow large in Lake Akan?
Marimo grow in the shallow area of the north shore of the Churui Bay at the depth of 2 - 3 meters. It is said that the unique topography of Lake Akan and strong winds ( around 10 m/s ) from south help them roll to grow into a globular shape through photosynthesis. On top of that, the rich mineral content of the water from the volcanoes help them grow bigger. Lake Akan is a miracle place that satisfies all conditions to make marimo larger.
It had long been thought that it would take 150 to 200 years for a marimo to reach the size of about 30 cm. Recent research however shows that they grow 3-4 cm. every year. In Lake Akan, over 30 cm marimo have found that could be about 10 years old.
Where to see marimo?
Marimo in Lake Akan have been listed in endangered species and they are strictly controlled and the visitors is not allowed to enter the marimo habitat except during "Marimo Festival" which takes place in October.
However. there are 2 facilities in Akanko Onsen for the visitors to see marimo.
Akankohan Eco-museum Center has an aquarium of marimo. Marimo Exhibition and Observation Center on the Churui Island also has a larger aquarium which allow the visitors to observe marimo in a half-wild manner.