Nagashima Dam

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 Anglo-Japanese Hydroelectric Company (日英水力電気, Nichiei Suiroku Denki) 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 Hayakawa Electric (早川電力, Hayakawa Denryoku). By the mid-1950s, several dams had been completed on the upper reaches of the Ōi River and its tributaries.

In September 1954, a typhoon caused flooding in the downstream reaches of the Ōi River, leading to plans being drawn by the central government in Tokyo for a new dam, which was justified as a "multipurpose" dam to provide industrial water, agricultural water in addition to flood control. Work was delayed due to lack of budget in the 1960s, with the construction of the Tōkaidō Shinkansen and Tōmei Expressway, but was given additional impetus due to the "Tanabata Flood" of July 1974 which flooded most of downtown Shizuoka.

Construction work began on the Nagashima Dam in 1972 and was completed by 2002 by a consortium of the Maeda Corporation, Shimizu Corporation and the Takenaka Corporation. Work was facilitated by the proximity of the dam to the Ōigawa Railway.