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Joshin’etsukogen NP, Gunma
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Completed in 1956, Nozori Dam was Japan’s first rock-fill dam. Builders used a rare trick: the impact of rocks tossed onto the 44-m-high structure helped compact the dam body.
Before the 1956 dam, natural Nozori Pond and its roughly 1-km-long wetland filled this valley. The reservoir raised the waterline about 26 m, submerging a rare bog formed as the old lake slowly filled in.
Before the reservoir, residents stocked Nozori Pond with loaches and carp, then camped by the shore to catch loaches. The seasonal catch went to Kusatsu’s hot-spring inns until about 1951.
Though Lake Nozori sits in Gunma, its water flows north through the Nakatsu and Shinano rivers to the Sea of Japan. The lake lies in mountains that divide the Tone and Shinano watersheds.
Lake Nozori receives water from more than its natural catchment: nearby streams, including one on Nagano’s side, are also routed into it. Their combined drainage area is roughly as large as the lake’s own basin.
An Iriyama schoolchild’s essay records a grandfather’s tale of a giant snake-like ja-tō that left Lake Nozori, dipped its tail at nearby Kenzuri Hole, then traveled to Lake Haruna. It is local folklore, not a geographic explanation.
Iriyama residents once cut mountain sedge together at a set time each autumn, using it instead of rice straw. They also gathered edible plants and wood for household utensils, taking goods to Kusatsu to earn cash.
A mountain hut stood beside the natural pond before the reservoir existed. Agatsuma and Takasaki mountaineering clubs joined Kuni village to build it in 1935; it was moved near Fujimi Pass in 1952.
A 1984 study documented natural rainbow-trout spawning at Lake Nozori: researchers observed 4 spawning pairs in an inlet of Nishibuta Stream, one of the lake’s tributaries.
The lake’s bright yellow Nozori-kisuge is not a separate species: it is the local name for zenteika, better known as the Nikko daylily. More than 300 alpine plant species grow around the lake.
Winter weather helps keep some hillsides open: prevailing northwesterly winds trigger avalanches on southwest-facing slopes, limiting trees while contrasting slopes remain wooded.
A survey of small shoreline wetlands recorded 2 sphagnum mosses never previously documented in Gunma Prefecture. These tiny bogs have botanical surprises beyond the lake’s famous flower meadows.
Not every flower patch grows where it always did: local conservation efforts transplanted komakusa to Mt Hachiken in 1993–95, then began annual plantings of shirane-aoi in a birch forest there in 1996.
