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The Tone River (利根川, Tonegawa^?) is a river in the Kantō region of Japan. It is 322 km in length (second longest in Japan after the Shinano) and has a drainage area of 16,840 km² (largest in Japan). It is nicknamed Bando Taro (坂東太郎, Bandō Tarō^?); Bandō is an obsolete alias of Kanto, and Tarō is a popular given name for the eldest son).

Kurihashi Water Level Observatory (June 2005)

It is sometimes regarded as one of the three greatest rivers of Japan (the other two are the Yoshino in Shikoku and the Chikugo in Kyūshū).

The source of the river is Mount Ōminakami (大水上山), which straddles the border between Gunma and Niigata Prefectures. It gathers tributaries and pours into the Pacific Ocean at Choshi city in Chiba Prefecture. The Edo River branches away from the river and flows into Tokyo Bay.

Major tributaries of the river include Watarase, Kinu, Omoi, and Kokai.

The river was once known for its uncontrollable nature, and its route was changed drastically whenever floods occur. It is hard to trace the ancient route of the river.

The river originally flew into Tokyo Bay, and the tributaries like the Watarase and the Kinu had the independent river systems. For the sake of water transportation and flood control, extensive construction began in the 17th century, when the Kanto region became the political center of Japan. The present route of the river was determined in the mass during the Meiji period. Its vast watershed is thus largely artificial.

The river was important transport until the advent of railway in the 19th century. It carried not only local products like soy sauce from Choshi, but also products from the Tohoku region, in order to save time and to avoid risk in the open sea.

Today the river has several dams to supply water for more than 30 million inhabitants of Tokyo metropolitan area.