毬藻 / Marimo

毬藻是天然的球狀綠藻。小球狀的毬藻在日本以及世界各地都有生長。然而，阿寒湖的毬藻特徵為特別大，超過直徑30公分的個體也沒有很稀奇。因此被指定為日本天然紀念物。因阿寒湖湖底的地形和波浪的方向等條件都具備之下造就生成的因素。在學術上也是非常貴重的綠藻。

Marimo (Lake Ball or Moss Ball in English) is a spherical green algae found in fresh water. While they can be found all over the world, those found in Lake Alan are special on account of their size. Some in Lake Akan grow to more than 30 centimeters in diameter, which is very unique. As such, marimo in Lake Akan has been designated as Special National Treasures of Japan. There are several factors in the forming of Marimo: the geographical shape of the lake bed, its depth, and the predominant direction of wind blowing from mountains surrounding the lake.