This is an event which began with activities to conserve the endangered marimo algae of Lake Akanko. Marimo algae grow in fresh water and gather in large numbers to form green spherical bodies. It takes more than 100 years for natural marimo algae to grow to a diameter of 10cm, but the marimo algae in Lake Akanko are the largest in the world, growing to a diameter of 30cm. They are designated as Special Natural Monuments.

This unique festival featuring marimo has developed into a major event of Hokkaido and is even referred to in the following way: "The Sapporo Snow Festival is the champion of festivals in Western Hokkaido and the Marimo Festival is the champion of festivals in Eastern Hokkaido." Both festivals were held for the first time in 1950.

Lake Akanko and marimo are closely associated with the indigenous Ainu people, who live mainly in Hokkaido, as is this festival.

On the first day of the festival, a lecture on the growth of marimo and field trips to their habitat are held. The second day features the Marimo Dance Parade, the Marimo portable shrine and the Ceremony for Receiving Marimo, along with the Ceremony to Conserve Marimo in accordance with ancient Ainu traditions. Upon receiving marimo, gratitude is offered to the gods of Mother Nature for the past year's blessings. The festival closes with the solemn Ceremony of Returning Marimo to the Lake, when marimo are carried on a canoe accompanied by an elderly Ainu chief and returned to the depths of the lake bed. 

At night, you can watch the Pine Torch Procession and the fireworks display. 

During the festival you can also enjoy all kinds of attractions on the grounds by the lakeshore, such as game competitions and the bazaar.