The Ōi River is a river in Shizuoka Prefecture, Japan. The Ōi River flows from the Akaishi Mountains, the branch of the Japanese Southern Alps which form the border between Shizuoka, Nagano and Yamanashi prefectures. These mountains, with peaks ranging from 2,000 to 3,000 metres, are characterized by heavy rainfall and deep V-shaped valley…The Ōi River is a river in Shizuoka Prefecture, Japan. The Ōi River flows from the Akaishi Mountains, the branch of the Japanese Southern Alps which form the border between Shizuoka, Nagano and Yamanashi prefectures. These mountains, with peaks ranging from 2,000 to 3,000 metres, are characterized by heavy rainfall and deep V-shaped valleys. The river follows a generally southern course, with seven wide bends in its central region, before exiting into Suruga Bay in the Philippine Sea.