There is a lake in eastern Hokkaido where a certain kind of algae grows into perfect green spheres. They are called marimo, and they are found nowhere else in the world in quite this form — a national special natural monument, and an endangered species. Once, they were nearly lost. Since 1950, a festival held each October has existed to protect them, and it is unlike any other festival you will attend.

Its structure is a sequence of ceremonies: one to welcome the marimo, one to safeguard them, one to send them back. The indigenous Ainu people gather at Lake Akan and offer the kamuinomi, a prayer to the gods, and the marimo are carried out onto the water in a dugout canoe and returned, gently, to the lake. There is something moving in watching a festival whose entire purpose is restoration — the giving back of something that was taken.

There is spectacle, too. A great torchlight procession moves through the lakeside town after dark, and troupes perform the old Ainu dances, the movements passed down across generations. By early October the autumn colors have begun to touch the shore, and against them the fire and the prayer take on a particular gravity.

Most festivals celebrate. This one protects. And in doing so it becomes, quietly, one of the most sincere gatherings in the north.