Marimo are filamentous green algae that get together in the shape of big moss balls. They live in a few rare lakes, among which lake Akan in Hokkaido where the biggest ones are to be found, up to 30 centimeters in diameter. The marimo algae is an endangered species and has been listed as a Natural Monument of Japan, which led to the organization in 1950 of a festival to protect it.
The Marimo Matsuri is also a tribute to Ainu culture and its rites enliven the three days’ celebration.
Celebrations are held from the second day with an Ainu dance parade, receiving and protection ceremonies of the marimo algae with a torch procession going from the lake to the Ainu village where a traditional danse competition is held. The next day, another procession starts the sending back of the marimo to the lake. Carried in a canoe, they are sent back into the depths of the lake by an Ainu chief.