Tonegawa

During spring snowmelt, paddlers from the Tokyo area flock to this section of the Tonegawa for some of the best whitewater within a day trip of the city. The primary season runs from April through June, when melting snow feeds the river and upstream dam releases help maintain fairly consistent flows. Even so, higher releases quickly transform the run into a powerful, pushy experience where rescue becomes difficult and swims can carry a long way downstream.

Minakami is better known as a hot-spring town at the base of the mountains in the far reaches of Gunma Prefecture. Ski slopes and traditional inns dot the surrounding hillsides, including the spectacular open-air bath at Takaragawa Onsen, and the contrast between alpine canyon and urban river corridor gives this run a distinctive character.

Within a few hundred meters of the upper put-in on the Yubisogawa you are flushed into the mainstem Tonegawa and immediately enter the canyon section. For roughly two kilometers the river delivers near-continuous whitewater, punctuated by two distinct Class IV drops. The first can be scouted from a bedrock island on river left. The line drives down the main tongue center-right through exploding waves and powerful hydraulics.

After more strong III+ water, the river drops into the second Class IV rapid. This one cannot be scouted from above. Work your way toward river right and avoid the “Room of Doom” eddy on river left. The canyon rapids are not especially technical, but the water is big, fast, and continuous. At snowmelt flows, a swim will likely continue to the railroad bridge at the bottom of the canyon. Eddies suitable for rescue are scarce, and there are even fewer places to empty and reenter a swamped boat.

This upper section is also the most scenic. The river slices through clean bedrock walls framed by mixed deciduous forest, with cold, clear snowmelt surging through a sculpted channel.

Below the railroad bridge the river opens slightly

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