Tamagawa Onsen （玉川温泉） is a hotspring located in Tamagawa area about an hour away from JR Tazawako Station. It is known for the most acidic mineral water found in Japan (P.H. 1.05) and for the largest amount of water produced from the headspring (9,000 liter/minute).
When you arrive at Tamagawa Onsen (take a bus from JR Tazawako Station or drive), the walkway is easily found located across from the buildings. Just follow the path and you will see it in a few minutes.
The strong acid water is rich in sulfuric acid, iron (II), aluminum, and chloride. The original water is transparent and no color, with odor from hydrogen sulfide. It is said to be most effective in sterilizing many kinds of germs that cause skin diseases.
Violent streams of hot spring water.
Yu-no-hana is the foam formed by crystalization of minerals in hot spring water.
The original temperature is 95 degree in Celsius (203 degree in Fahrenheit), which cools down to 39 degree in Celsius (102 degree in Fahrenheit). The water along with the bedrock is radioactive, which is also another reason why the hot spring is particularly popular for people under specific treatment. The public bathing area is located in the building.
The headspring can be seen from a walkway over the fence. Please remember that the volcanic activity is caused unpredictably with emission of natural gas and acid steam, so do not for an extended period of time.
Fumaroles (sulphur vents) are found near the headspring