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Fuji-Hakone-Izu NP, Kanagawa
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About 3,000 years ago, a huge collapse on Mt. Kamiyama dammed the Hayakawa River inside Hakone’s caldera, forming the lake we see today. Ashinoko is, in effect, a natural landslide dam.
In ordinary conditions, Ashinoko’s water heads west to Shizuoka—not down the nearby Hayakawa—through a 1,280-m hand-dug tunnel completed in 1670. Workers digging from both ends met with only about 1 m of level difference.
On October 1, the first Ashinoko wakasagi catch is offered at Hakone Shrine and presented to the Imperial Household. The lake’s small smelt also becomes kanroni, slowly simmered into a glossy local New Year favorite.
Ashinoko’s fishing cooperative has developed a natural-spawning tank method for wakasagi. Its eggs are now supplied to around 20 other lakes, making this mountain lake an important nursery far beyond Hakone.
Today’s wooded west bank was once open grassland: in the Edo period, it was kept clear by burning so guards at Hakone Checkpoint could watch travelers around the lake. Later planting created the forest seen today.
Hakone’s sacred story begins with a nine-headed lake dragon: legend says the 8th-century monk Mangan pacified it, and it became Kuzuryu, the lake’s guardian deity, still revered at Hakone Shrine.
On July 31, an offering boat carrying only Hakone Shrine’s chief priest travels to the lake’s center for the Lake Water Festival. The offering includes nearly 6 L of red rice, measured as 3 shō, 3 go and 3 shaku; fireworks follow.
The lake’s Peace Torii was erected in 1952 to mark Japan’s independence and Crown Prince Akihito’s investiture. In 1964, a plaque reading “Peace,” written by former prime minister Yoshida Shigeru, was added.
A travel diary from 1242 calls it both “Hakone’s water sea” and “Ashi no umi”—the Sea of Reeds. The familiar reading Ashi-no-ko came later; for centuries, people called this inland lake a sea.
Ashinoko’s January 5 lake-opening rite includes a priest skiing across the water in ceremonial robes to purify it. The custom honors the lake’s place in Japan’s water-skiing history.
Lake Ashi was the first place largemouth bass were introduced in Japan: fish from North America were released here in 1925. The species later spread widely across the country.
Ashinoko is said to mark the southern edge of the landlocked sockeye salmon’s range in Japan. The fish, called himemasu, was first transplanted here from Lake Towada in 1909.
A dace native to Ashinoko carries the lake’s home in its scientific name: Tribolodon hakonensis. The species was named from specimens collected here.
