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Nikko NP, Gunma
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Marunuma was a natural lake before the dam was built in 1931. The water level rose about 28 m, expanding a 600 m-long oval into today’s lake, roughly 1.2 km long and 500 m wide.
Rainbow-trout farming began here in the Meiji era; by the Taishō era, aristocrats and business leaders came to fish. Today, the lakeside inn serves charcoal-grilled yamame trout with local maitake mushrooms.
Its concrete wall is braced by buttresses, a design that saves material. Japan built only 8 such dams in the early Shōwa period; 6 survive, and Marunuma is the largest. It still generates power and is a National Important Cultural Property.
Marunuma is a lava-dammed lake: flows from Mount Nikkō-Shirane blocked a stream and created it. The lake’s volcanic origins came long before the hydroelectric project made use of its water.
Marunuma’s hot-spring area inspired Kōda Rohan’s 1890 ghost story “Taidokuro” (「対髑髏」). It predates the 1931 dam, so its setting was the smaller, natural lake.
Water from upper Sugenuma first passes through Marunuma Power Station, then flows into Marunuma. The dam stores water for use farther downstream at Ichinose Power Station—a chain built around lakes that existed naturally.
At lakeside Kankōsō, a trout sculpture in the Rainbow Trout Bath pours spring water from its mouth. A nearby tank holds live rainbow trout, carrying Marunuma’s fishing theme right into the bathhouse.
