Oyachi Marsh was added to Your Favorites!
Myōkō-Togakushi Renzan NP, Nagano
Claim this place to tell your story your way.
On the slope above Oyachi, the nearby Kamigeya Paleolithic site yielded 708 stone tools and 4 clusters of fire-cracked stones—likely cooking spots. The camp dates to about 20,000 years ago.
Tools from the nearby site tell of distant connections: obsidian is thought to have come from Wada Pass and shale from Niigata. Knife-making styles also echo traditions from across northern, eastern and western Japan.
Oyachi’s open outlook makes Iizuna’s smooth, broad volcanic shape easy to see. Elsewhere in the park, the jagged Togakushi peaks formed differently, from ancient seafloor rock that was uplifted.
Yellow flag iris looks lovely, but this non-native plant spreads by tough rhizomes and has displaced habitat for Oyachi’s marsh marigold. Local volunteers have been digging out its roots since 2012.
Oyachi’s spring display is more than skunk cabbage: marsh marigold and two-flowered anemone bloom alongside spring ephemerals such as hitotsu-shizuka, shōjō-bakama and Azuma-ichige.
In winter 2017–18, 146 Nagano City staff spent 10 workdays removing 8,270 kg of reeds from Oyachi. The whole haul was put to use as fuel for biomass power generation.
Wetlands gradually transition toward forest over time, and Oyachi’s reeds and trees are contributing to drying. Local reed-cutting helps preserve the open, wet habitat where its spring flowers grow.
To study drying at Oyachi, a Nagano Kosen research project paired drone imagery for 3D vegetation models with cone tests measuring ground firmness, examining how the ground and reed growth relate.
On a spring patrol, a park ranger noted a great spotted woodpecker drumming in the woods behind the marsh, along with narcissus flycatchers and Eurasian wrens—a lively bonus beyond the flowers.
