Marimo at Akan Kohan Eco Museum Center

One goal to come to this Lake Akan was to get Marimo back. Marimo is a species of green alga that lives in freshwater lakes. Marimo in Lake Akan were first discovered by Tetsuya Kawakami in 1897, and named marimo because of their spherical shape.

In 1921, they were designated a Natural Monument, and a Special Natural Monument in 1952 by the government, aiming to preserve the species. In 1997, however, they were classified as Critically Endangered-the most endangered species-in the Red List announced by the government.

Marimo are versatile in habitat; other than its spherical form, they sometimes cling to rocks and shells, or drift along on the lake bottom like cotton fluff. Marimo are distributed mainly in high-latitude areas of the northern hemisphere, and have been confirmed inhabiting more than 10 lakes in Honshu and Hokkaido including Lake Akan.

Lake Akan, however, is the only lake in Japan which spherical marimo inhabit in communities. Diversity in living form, such as spherical shape, is caused by many environment factors, which means Lake Akan is the only place with all the elements required for spherical marimo to develop.

If you look at a cross section of a marimo, algal filaments spread in a radical pattern, which indicates how it developed into a ball as the center of the algae grew toward the outside.

How do marimo become spherical?

  1. When a large spherical marimo is broken by waves. it falls into many wedge-shaped pieces.
  2. These pieces grow into smal oval aggregations.
  3. When an aggregation develops further, it gradually becomes ball shaped.
  4. As they  increase in size, marimo move inch by inch to deeper places offshore by the water current. When they go deeper, parts of the algae wither because sunlight does not fully reach the lake bottom, and gradually their shapes break down.
  5. Larges-sized marimo are sometimes washed to the shallow ends. They break just as they do when they move offshore, but since plenty sunlight comes through in shallows areas, they can begin growing again.

The Marimo festival is the largest festival of Lake Akan, which began in 1950 for the conservation of marimo. As a forerunner to nature conservation movements in Japan, the festival still continues with the intention of expressing our gratitude to Mother Nature through marimo. This spectacular but solemn festival, including fireworks, a ceremony to return marimo to the lake from a dugout canoe and folk performances by Ainu dancers gathered from all over Japan, is held in mid-October with Lake Akan’s autumn colors in background.

Source: Akan Tourist Association (a leaflet that I got from Akan Kohan Eco Museum Center )


A fish in a tank at this center


I bought two marimo back from a souvenir shop closed by. It likes cold place and some sunlight.

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