Yanba Dam

Yanba Dam is a concrete structure on the Agatsuma River in Naganohara town, Gunma Prefecture. The gravity wall reaches 131 meters in height and 291 meters in length, holding back water that forms a reservoir surrounded by forested hills.

Planning for the structure began in 1952 with initial surveys of the valley, but delays and modifications stretched the project over more than six decades. The completed facility opened in March 2020 and now regulates the flow of the Agatsuma River.

The reservoir takes its name from the Agatsuma River, whose waters now gather behind the concrete wall and form a recreational area for nearby towns. Visitors find picnic spots and walking trails along the wooded slopes, where the calm water reflects the surrounding forested hills.

Multiple elevators connect the upper level to the Agatsuma Valley below, allowing visitors to descend without long staircases. Guided tours run daily between 9 in the morning and 5 in the afternoon, and an information center provides insight into the function and engineering of the structure.

Staff distribute special collector cards featuring the structure and its technical details to visitors, and these souvenirs have become popular with enthusiasts across Japan. The adjacent café serves green melon soda topped with soft ice cream, and the colors recall the turquoise water of the reservoir.

Location: Naganohara

Inception: March 31, 2020

Height: 131 m

Part of: 利根川上流ダム群

Website: https://ktr.mlit.go.jp/tonedamu/tonedamu_index004-1.html

GPS coordinates: 36.55694,138.71417

Latest update: December 12, 2025 21:15