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Kushiro Shitsugen NP, Hokkaido
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Even below −20°C, springs along Onnenai’s old railbed can stay unfrozen. Black-backed wagtails have been recorded feeding there in winter, although Hokkaido usually counts them as summer visitors.
The center displays a real yachibozu cross-section. These “bog monks” are sedge mounds: winter frost lifts their root clumps, spring melt wears away the bases, and the cycle gradually builds them up to 40–50cm.
Part of the marsh route follows the former Tsurui village railway. Opened in 1928 and closed in 1968, it carried people and goods—including tofu from Kushiro; today, its old trackbed leads walkers into the wetland.
After dark, the boardwalk has a summer spectacle of its own: Heike fireflies may be seen around Onnenai in July and August, glowing in the same wetland landscape that visitors explore by day.
The center’s 2013–2021 bird inventory lists a wandering fieldfare at Onnenai on just 2 dates: March 27, 2015, and March 16, 2019. It’s a reminder that even a familiar trail can host a surprise visitor.
The Onnenai boardwalk opened in 1990, 2 years before the original visitor center. Its wider route crosses alder forest, reed-and-sedge marsh, and sphagnum bog, with about 2km designed for wheelchair access.
On a March 2026 history walk, old photos showed that the boardwalk entrance had once been almost treeless. Today, alder and Japanese ash grow there—a change visible even before the marsh walk begins.
Since 2013, visitor-center staff have recorded birds during their patrols, noting the first spring arrival of summer visitors and mapping singing males to follow breeding activity. The observations also appear in a monthly local newsletter.
A local wetland research report gives several interpretations of the Ainu place-name 温根内 (Onnenai): “large river,” “old river,” or “river with many tributaries.” Each reading ties the name to water.
