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Hidakasanmyaku Erimo Tokachi NP, Hokkaido
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Japan’s Geospatial Information Authority lists the headwall of Hachi-no-sawa on the Satsunai as an ice-carved valley—and maps another at Jū-no-sawa. These source-stream walls were sculpted by glaciers, not just running water.
In 1962, students from Obihiro Daiichi Junior High held a “kawagari” outing on the Satsunai: they caught fish, grilled them over driftwood gathered in the riverbed, and cooked rice with river water. It was a school tradition.
Ainu sat-nay means “dry river”—a name that fits the Satsunai’s gravel fan downstream: in low-water seasons, surface flow can vanish into the stones, then feed groundwater and smaller spring-fed streams.
The upper Satsunai is one of Japan’s largest native habitats for keshōyanagi, a glacial-age willow. It favors sunny gravel banks with groundwater, and shifting riverbeds create open ground where its seedlings can take hold.
These headwaters feed a river selected 10 times among Japan’s rivers with the most favorable water quality: 8 annual selections from 1991 to 2005, then again in 2024 and 2025.
Satsunai water supports daily life far downstream: it supplies 1 city, 4 towns and 2 villages. In Nakasatsunai, about 80% of farmland uses the river’s water for irrigation and crop spraying.
Japan’s national natural-environment survey lists the upper Satsunai mainstem, Nana-no-sawa and Go-no-sawa as “primitive watersheds.” The mainstem basin alone spans 3,990 hectares and rises from 620 to 1,979 m.
