Tamagawa Hot Spring
- Location
- Tamagawa, Japan
- Water type
- carbonated, radioactive, acidic
- Temperature
- 35 °C
- pH
- 1.2
Water profile
Soothing — neither hot nor cold, perfect balance.
Rich in active gases or metals — a strong mineral character.
Mineralised water — eases movement and joints.
Tamagawa Hot Spring is one of Japan's most celebrated hot springs, located in a remote volcanic valley in Semboku City, Akita Prefecture, where highly acidic carbonated-radon water of extraordinary mineral concentration flows from a single source at temperatures around 98°C — reputedly the most acidic natural hot spring in Japan at pH approximately 1.2. The waters, known for their remarkable concentrations of carbonic acid and mild natural radioactivity from radon, have been part of a long thermal tradition for over 300 years, with carefully timed bathing in keeping with their acidity. Tamagawa's deeply remote mountain setting and the steaming moonscape of mineral-deposited stone around the source create an experience unlike any other onsen in Japan.