Mari is a type of bouncy play ball; mo is a generic Japanese term for plants that grow in water.

[citation needed] The algae has three growth forms: The existence of marimo colonies depends on the adaptation of the species to low light conditions, combined with the dynamic interaction of wind-induced currents, light regime, lake morphology, bottom substrate, and sedimentation.

[2] The balls are green all the way round which guarantees that they can photosynthesize no matter which side is turned upwards.

[2] The species is mainly found in the areas of Europe previously covered in glaciers (Northern-Europe), and in several places in Japan.

An excess of nutrients (due to agriculture and fish farming), along with mud deposition from human activity are thought to be the main causes for its disappearance from many lakes.

In Japan, the Ainu people hold a three-day marimo festival every October at Lake Akan.

[citation needed] A widely marketed stuffed toy character known as Marimokkori takes the anthropomorphic form of the marimo algae as one part of its design.

[2] Balls sold in Japanese aquarium shops are of European origin,[2] as collecting them from Lake Akan is prohibited.

[7] In the manga One Piece and its adaptation, the Straw Hat Crew's swordsman, Zoro, is often referred to as "Marimo Head" due to his spiky green hair.

On 2 March 2021,[8] the United States Geological Survey was notified that zebra mussels had been discovered in moss balls sold in pet stores across North America.

[10] Owners of fish tanks were urged to decontaminate the moss balls by boiling, freezing, or bleaching them before disposing of them to prevent spread to local waterways.