The Hatanagi-II is a dam on the Ōi River in Aoi-ku, Shizuoka, Shizuoka Prefecture on the island of Honshū, Japan. A hollow-core concrete gravity dam, it has a hydroelectric power generating station owned by the Chubu Electric Power Company. The Hatanagi Project was designed as a Pumped-storage hydroelectricity facility, with the discharge from Hatanagi-I discharging through a five kilometer penstock into a lake created by the smaller Hatanagi No.2 Dam downstream.
The reversible turbine generators at the Hatanagi No.1 power plant were designed to function as either electrical power generators, or as pumps, to reverse the flow of water back into the reservoir in times of low demand. The generators at the Hatanagi No.1 power plant have a capacity of 137,000 KW, and a maximum flow rate of 137 m3/sec. The Hatanagi No.2 power plant adds an additional 85,000 KW to the electrical grid of the Tōkai region of central Japan.