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Shikotsu-Tōya NP., Hokkaido
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Lake Kuttara once held Ezo salamanders that became fertile while still keeping larval gills and tail fins. First reported here in 1924, this unusual population was last recorded in 1932; the rare life stage was later found again elsewhere in Iburi.
Tome Nakao arrived in 1909 to help raise kokanee. Her husband returned to Sapporo, but she stayed by the lake until her death in 1942, later riding horseback in Western clothes to sell charcoal in Noboribetsu.
A 1921 local record describes a Lake Kuttara kokanee (hime-masu) measuring 75 cm and weighing 4.5 kg. The fishery grew from early stocking efforts using fish from Lake Towada and Lake Shikotsu.
In a Shiraoi Ainu tradition, elders said thunder was the sound of a thunder deity rising from Kuttarushito, and offered sake to the god believed to dwell beyond Noboribetsu during important ceremonies.
In the Environment Agency’s 1991 survey, Lake Kuttara’s water clarity measured 22.0 m—the second-highest reading among the surveyed Japanese lakes, behind Lake Mashu. A 2022 measurement was 19.3 m.
Lake Kuttara’s first lake festival was held in 1955, with floating lanterns, fireworks and boat races. A sightseeing boat, the Hakucho Maru, also carried visitors on the lake until around 1960.
Lake Kuttara’s round shape is more than an impression: a 1991 survey gave it a shoreline-shape index of 1.01, where 1.00 represents a perfect circle. It ranked as the roundest among Japan’s caldera lakes.
No major river flows into or out of Lake Kuttara. Instead, research describes groundwater seeping away toward the Ayoro River. People in Noboribetsu once thought the lake supplied their hot springs, but the water takes a different underground route.
The lake’s conservation value extends below the surface: it is habitat for katashajikumo, a freshwater alga listed as Threatened I in Japan’s 2020 Red List. The Environment Ministry also includes Lake Kuttara among its Important Wetlands.
Lake Kuttara covers only 4.7 km², yet plunges to 148 m—the third-deepest natural lake in Hokkaido. Its deepest point is about 900 m from the eastern shore, where the caldera floor drops away.
The name Kuttara is linked to the Ainu place-name Kuttarushito, commonly interpreted as “the lake by Kuttarushi,” a place associated with knotweed. The same plant-name root appears in nearby Kojohama, or Itadori Beach.
Lake Kuttara once froze completely each winter, sometimes forming omiwatari—raised ice ridges made as the ice presses shoreward. A 2017 study noted 4 winters since 2000 when the lake did not freeze over completely.
