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Shikotsu-Tōya NP., Hokkaido
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Near the north shore, researchers found Thioploca ingrica—large sulfur-oxidizing bacteria whose sheaths can reach several centimeters. Lake samples helped produce the first complete genome for this bacterial group.
Mt. Eniwa, rising beside Okotanpe, hosted downhill skiing at the 1972 Sapporo Winter Olympics. After conservation protests, its temporary course was removed and the slopes replanted.
Okotanpe is no volcanic crater: eruptions of nearby Mt. Eniwa sent material that dammed the Okotanpe River, forming the lake beside the much larger Shikotsu caldera.
Okotanpe's name first belonged to the river, not the lake. Hokkaido researchers trace it to Ainu and gloss it as a river with a dwelling at its lower end; the lake later took the river's name.
The lake drains in dramatic fashion: its outflow drops as a waterfall into the Okotanpe River, which carries the water about 360 m downhill to Lake Shikotsu.
Okotanpe can appear emerald green or cobalt blue as weather, sunlight, and viewing angle change. In early spring, broken snowmelt ice can even look like drifting sea ice.
This remote-looking lake has a hidden wetland neighbor: its western shore holds a sedge-rich marsh, while Ezo salamanders live in the lake itself. Both lie within a special protection area.
Every bit of Lake Okotanpe's 8.62-km² watershed is forest or other natural land, according to Hokkaido's lake researchers. No developed land drains into this protected basin.
