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Nikko NP, Tochigi
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In 1928, a fire swept through Yumoto Onsen and about 100 brook trout escaped from an inn’s garden pond into Lake Yunoko. They bred naturally, helping establish the lake’s brook-trout population.
“Yunoko” means “hot-water lake,” and the name fits: hot-spring water wells up through the lakebed. In the northeast bay, those springs help make the lake an important winter stop for ducks.
Lake Yunoko’s water plunges over 70-meter Yudaki Falls, winds through Senjogahara, passes Ryuzu Falls, and eventually reaches Lake Chuzenji. One small lake feeds a remarkable string of landscapes.
Lake Yunoko’s outlet, the Yukawa, became a birthplace of Japanese fly-fishing. In 1902, Thomas Glover arranged 25,000 brook-trout eggs from Colorado; a typhoon killed the first fry, but a second release survived.
Lake Yunoko’s only peninsula is Usagijima, or “Rabbit Island”—named for its rabbit-ear shape. A small wetland at its base grows cotton grass and bog cranberry, adding a quiet wildlife-rich corner to the lakeshore.
Local tradition traces the hot-spring village on Yunoko’s north shore to 788, when the monk Shodo is said to have discovered a spring and named it Yakushi-no-yu. The lake’s name grew from this same hot-water landscape.
Since 1998, people have worked to remove invasive waterweed from Yunoko. In the hands-on cleanup, helpers cast anchors from boats to snag plants on the lakebed, then haul the weed ashore to protect water quality.
Yumoto wastewater and hot-spring inputs once helped build sludge, and the lake’s transparency fell to 1.8 meters. After careful sludge-suction work began in 1992, it had improved to 3 meters by August 1994.
Lake Yunoko is part of a 260.41-hectare Ramsar wetland—not a standalone lake reserve. Registered in 2005, the site also links the Yukawa River with the marshes of Senjogahara and Odashirogahara.
On May 1, 2026, fireworks signaled Lake Yunoko’s trout-season opening at 5:00 a.m.—a wonderfully dramatic starting bell for an early-morning fishing day.
