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Kushiro Shitsugen NP, Hokkaido
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“Hishikui” means “hishi eater”: these migratory geese really do feed on water-chestnut fruits at Shirarutoro. Park staff counted 896 here on October 16, 2015, as birds paused on their journey south from Kamchatka.
Nearby Tōro Kotan’s Ainu held Pekanpe Kamuy-nomi to thank the kamuy for hishi nuts and pray for a safe harvest before gathering by canoe. The nuts were boiled or dried for food; Shibecha records the rite until around 1990.
Shirarutoro is more than 20 km from the sea today, yet it began as part of an ancient bay. As the shoreline retreated and rivers freshened the water, this lagoon remnant survived among the lakes left about 3,000 years ago.
Two Ainu chashi sites named Shirarutoro 1 and 2 belong to the Kushiro River Basin Chashi Sites, a nationally designated historic group. They were added to the protected group in 2015.
Shirarutoro usually drains into the Kushiro River, but heavy rain can reverse the flow when lake levels are low, sending river water back into the lake. Researchers have documented this surprising two-way connection.
A summer 2023 drone survey estimated that hishi covered 54.6% of Shirarutoro. Researchers also suggest a curious loop: dying plants settle on the bottom, create shallows, and may help the next hishi crop spread.
A 2007 survey recorded 23 native aquatic-plant species in Shirarutoro, including 4 then listed on Japan’s Red List. In the south, however, hishi dominated broad patches of the lake.
In 1858, explorer Matsuura Takeshirō recorded local communities and drew Shirarutoro-numa in his survey diary—a rare written-and-sketched snapshot of the lake and its surroundings.
A stretch of lakeshore near Reisen Bridge stays unfrozen in winter, attracting waterbirds even in the cold season. Shirarutoro is also a busy spring and autumn stopover for migrants traveling between Siberia and Japan.
The Ainu-derived name Shirarutoro is interpreted in Hokkaido’s place-name dictionary as “a stream running between rocky shores”—a waterway description tucked into the name of a lake.
Nearby, Butterfly Forest was deliberately planted with flowers and trees favored by butterflies. Across Kushiro Marsh, 84 butterfly species have been recorded, with different kinds using its grasslands and woods.
