Ushiwatari River runs about 4 km along the edge of volcanic rock from Mt. Chokai. The river is sourced almost entirely by spring water, springing out through cracks between the rocks. 24 tons of water are estimated to flow from these springs per minute.
The water here keeps a year-round temperature of about 11℃. Because of this, in early summer you can see the aquatic plant baikamo (Ranunculus nipponicus var. submersus) swaying on the river’s surface, its small white flowers blooming beautifully. The river is also home to species of sculpin fish, and every year in autumn, large numbers of salmon can be seen swimming upriver to spawn.

Maruike-sama Pond is about 20 m in diameter and 3.5 m deep. It is also made up of nearly 100% natural spring water. If you look closely, you can see the sand on the bottom of the pond moving, seeming to swirl as the water springs up from below. Because the water maintains a temperature of about 11℃ year round, tree branches that fall into the pond take a very long time to decay.
The blue-green color of the pond adds to its mysterious atmosphere. Nearby is Maruike Shrine, which enshrines the pond as an object of worship and was designated as a National Historic Site in 2008. The local people call this pond “Maruike-sama,” always using the honorific suffix “-sama” to express their reverence.