Nagatoro Iwadatami River Shallows

The Iwadatami rock shelf at Nagatoro forms a broad, flat expanse of banded chert bedrock in the Arakawa River, and the shallow pools that collect along its edges give this stretch of Chichibu District its unofficial status as a swimming spot. Rather than sand, visitors wade on smooth, water-worn rock and fine river gravel; the water runs clear and cool, tinted pale green-grey where it pools over the dark rock strata that give Iwadatami its 'thousand-tatami-mat' nickname. The shallows sit close to the riverbank in a gently curved pocket shielded from the main current, so exposure to wind and surf is minimal compared with the open channel just a few meters away, where traditional kotori-bune boats and commercial rafting trips pass through faster water. The overall vibe leans family and casual day-tripper rather than surf or party: groups wade, splash, and picnic on the flat rock in summer, while rafting outfitters and boat operators occupy the deeper channel. Amenities are limited directly at the water's edge — there are no sun loungers or a staffed lifeguard station — but restaurants, souvenir shops, and public restrooms cluster a five-minute walk away near Nagatoro Station, and the riverside footpath along the rock formation offers shaded rest spots. Access is straightforward: Nagatoro Station on the Chichibu Railway sits a short, flat walk from the rock shelf, making this one of the more transit-friendly river swimming spots in Saitama, though summer weekends draw sizable crowds of rafters, boaters, and waders competing for the same stretch of river.