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.
The river was once known for its uncontrollable nature, and its route was changed drastically whenever floods occurred. It is hard to trace the ancient route of the river.
The river originally flowed into Tokyo Bay, and tributaries like the Watarase and Kinu had 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.
Minakami Onsen in Gunma Prefecture, is the source for the Tone River and during the Spring snow melt period, April - June, the river provides consistent grade 4 rapids (on the International Scale of River Difficulty) over a 12km stretch. The river provides some of the best white water rafting and kayaking in Japan and played host to the rafting world cup in Spring 2007. The snow melt swells the river to grade 4 in Spring; in the Summer it is a gentle grade 2. The MomijiKyo section has 7 grade 3-4 rapids in 1 km and is 12 km long in total.