Lake Okuyahagi located near the southern border of Gifu Prefecture is a dam lake formed by Yahagi Dam constructed in 1970. It functions as the downstream reservoir of Yahagi- Daiichi (No.1) and Daini (No.2) Electric Power Plants, which employs pumped-up hydropower. It is always full of water and provides water for the surrounding areas.

Nature remains intact in the area around the lake. A variety of small animals inhabit in the mountains, while Amago and pale chub live in the clear stream. The landscape of the lake changes from season to season. A lot of visitors come to enjoy cherry blossoms in spring and autumn leaves from mid to late November. It is the scenic spot, where various outdoor activities can be enjoyed.