大井川
The potential of the Ōi River valley for hydroelectric power development was realized by the Meiji government at the start of the twentieth century. The Ōi River was characterized by a high volume of flow and a fast current. Its mountainous upper reaches and tributaries were areas of steep valleys and abundant rainfall, and were sparsely populated. In 1906, a joint venture company, the was established, and began studies and design work on plans to exploit the potential of the Ōi River and Fuji River in Shizuoka Prefecture. The British interests were bought out by 1921, and the company was renamed . By the mid-1950s, several dams had been completed on the upper reaches of the Ōi River and its tributaries.