Marimo is a species of green algae (Cladophora sauteri) that forms in spherical balls.
First discovered in 1823 by Dr. Anton E. Sauter in Lake Zeller in Austria, marimo can be found in a number of lakes in the northern hemisphere including Lake Akan in northern Hokkaido.
Every October a marimo festival is held at Lake Akan led by local Ainu elders. The marimo has been protected in Japan since 1921. The Marimo Exhibition and Observation Center was built on the shores of Lake Akan in the 1970s and renovated in the 1990s.
These marimo were photographed in a tank in the Tanuki-koji covered arcade in the Susukino district of Sapporo.
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