Kinugawa River, Kinugawa, or Kinu River(鬼怒川,Kinugawa?), is a river on the main island of Honshu in Japan. It flows from the north to the south on the Kantō plain, merging with Tone River(利根川,Tonegawa?). At 176.7 km in length, it is the longest tributary of Tonegawa. From ancient times, it has been known to cause floods. The river starts in Kinu swamp in the city of Nikkō, Tochigi, within Nikkō National Park.