Chugging tour boats with noisy Japanese commentaries and even speedboats disturb the waters between the smoking volcanoes Me-Akandake and O-Akandake (He-Akan and She-Akan). But out on Churui Island, silence is green among Akanko's strangest inhabitants, marimo, as they nestle peacefully in display tanks. Marimo are spherical colonies of green algae that may be as small as a Ping-Pong ball or as large as a soccer ball (the latter taking up to 500 years to form). Rare life forms, marimo can only be found in Lake Yamanaka, near Fuji-san, and in a few lakes in North America, Siberia, and Switzerland. These strange algae act much like submarines, bobbing to the lake surface when bright sunshine increases their photosynthesis, then diving below during inclement weather when light levels drop. Nearby shops offer them in bottles.
While you're in the area, take a look at Mashu-ko one of the world's clearest lakes, visible only from afar (if at all, as it's often shrouded in fog). Kussharo-ko is less impressive, but you can enjoy a hot sand bath on the lakeshore just north of Ikenoyu Onsen. Japanese travelers often take in all three lakes on the same trip.