Kinugawa River, Kinugawa, or Kinu River(鬼怒川,Kinu-gawa?), 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,Tone-gawa?). At 176.7 km in length, it is the longest tributary of Tone-gawa. 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.