The Hatanagi-I (畑薙第一ダム, Hatanagi dai-ichi damu) is a dam on the Ōi River in Aoi-ku, Shizuoka, Shizuoka Prefecture on the island of Honshū, Japan. With a height of 125 metres (410 ft), it is the tallest hollow-core concrete gravity dam in the world. It has a hydroelectric power generating station owned by the Chubu Electric Power Company.