Akan marimo is a unique type of algae found in the waters of Lake Akan in Hokkaido, Japan. These spherical green balls are formed by the growth of a specific species of algae called Aegagropila linnaei. They can grow up to 20 centimeters in diameter and are considered a natural treasure of the region. The formation of Akan marimo occurs when water currents cause the algae to roll and clump together, creating their distinctive shape. They thrive in clean, cold water and are often associated with local folklore, symbolizing good luck and longevity. Conservation efforts are in place to protect these rare organisms.