The headwaters of Himekawa River are located across the Aragami Forest on the north side of Oyakai Marsh. Himekawa River, which is fed by spring water, flows parallel to National Route 148 for a distance of 58 km and empties into the Sea of Japan at the mouth of Itoigawa City in Niigata Prefecture. In Japan, it is rare for the headwaters of a major river to flow along a national highway.