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 20th 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 . As early as the late 1920s, developers began to turn their attention to various tributary streams of the Ōi River, especially the Sumata River, with its steep-sided gorge and considerable flow volume.