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Kushiro Shitsugen NP, Hokkaido
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At Kayanuma, a 2.4-km stretch of the Kushiro River was restored to its former winding course in 2011. Monitoring found more fish and invertebrates, and more kinds of each, in the restored reach.
Shishamo, a fish found only in Japan, return to the Kushiro river system to spawn in autumn, including in the downstream Shin-Kushiro channel. Their roughly 8-mm fry hatch in spring and drift to the sea in about a day.
After a devastating flood in August 1920, engineers began cutting an 11.2-km outlet from Iwaoboki. The new Shin-Kushiro channel, completed by the early 1930s, diverted the main flow away from downtown Kushiro.
Salmon was a vital food for Ainu communities around Kushiro. A local study records the Ainu names sipe, meaning “real food,” and kamuy cep, “divine fish”; autumn’s abundant catch could be preserved for winter.
About 400 archaeological sites, from the Paleolithic period through the Ainu cultural era, cluster around the wetland’s eastern lakes and the Kushiro River. The raised banks offered useful routes and access to food.
In one Kushiro River tributary, surveys counted 2 Sakhalin taimen spawning nests in 2018 and 18 in 2019, after fishways improved access to upstream spawning grounds for this endangered giant of Japan’s fresh waters.
Kushiro’s local museum documents Ainu clothing made not only from mammal hides and bird skins, but also from salmon and taimen skins—two fish of the Kushiro River system.
Before rail took over, the Kushiro River carried people and supplies between the inland and the port. Timber was floated downstream, and steam riverboats began linking Shibecha and Kushiro in 1916.
The Kushiro River runs about 154 km from Lake Kussharo to the Pacific without artificial dams or weirs—a rarity in Japan. Its headwater lake and the wetland below also help keep its flow relatively steady.
The Kushiro wetland does more than surround the river: during floods, it stores water and helps protect the city downstream. Low cross-levees have been added to increase this natural flood-storage effect.
The river was once called Kusuri, but its name’s meaning is debated. One explanation links it to hot springs near Lake Kussharo; another reads the Ainu words kush-pet as a river-route connecting waterways.
