The high acidity of the water (pH around 2.0) is strong enough to dissolve pennies if submerged for several days.
The wooden troughs are constructed without using a single metal nail, as the acidic water would corrode iron instantly.
The water is piped directly from the source to various local ryokans and public bathing facilities.
The unique mineral composition of the water is traditionally believed to heal all illnesses except lovesickness.
The reservoir design mimics a landscape garden to manage the cooling process while serving as a civic gathering space.
The town of Kusatsu is situated at an elevation of approximately 1,200 meters, contributing to cooler ambient temperatures.
The 'Yumomi' practice developed to cool the water for bathing without diluting it with cold water, which would reduce its medicinal properties.
Yubatake is the primary hot spring source for the Kusatsu Onsen resort, channeling approximately 4,000 liters of geothermal water per minute. The reservoir consists of a complex system of wooden chutes designed to cool the naturally scalding 70-degree Celsius water to a bearable temperature for downstream public baths. It serves as the town's central plaza and architectural focal point. The site features a stepped waterfall and a surrounding stone-paved promenade. Sulfuric steam continuously rises from the water surface, creating a distinctively pungent aroma and thick mist. Yubatake is recognized as one of the most productive hot spring sources in Japan by total volume. Its water is noted for high acidity, which gives the spring its characteristic bright blue color. The reservoir is illuminated nightly to highlight the steam and fluid movement. It serves as the hub for the town's historic 'Yumomi' water-stirring tradition.
The raised viewing deck overlooking the waterfall at the bottom of the chutes.
Bring a towel to use at the free footbaths located at the lower end of the reservoir.
Visit after dusk to see the reservoir illuminated, which creates a more dramatic atmosphere than in daylight.
Wear shoes with good traction, as the steam and mist can make the stone pavement slippery.
Do not attempt to touch the water directly at the source, as it is dangerously hot.
Avoid throwing coins into the reservoir; remain on the designated walkways to avoid exposure to high-temperature steam.
