Yoshigadaira Wetlands are located in the centre of Honshu Island on the north-east flank of Mount Kusatsu-Shirane, an active volcano that erupted eight times in the 30 years to 2015. The Site comprises a group of moors, ponds, a lake and a stream which developed on low-permeable layers, depressions and a crater created by the volcanic activities.
The Site is unique because of the high temperature and acidity from the volcano and volcanic gases such as hydrogen sulphide. The water of the Anajigoku stream is extremely acidic (pH 2.6-2.8) with abundant iron and sulphur, but it hosts the largest community of the aquatic liverwort Jungermannia vulcanicola in East Asia. The water of Yugama, a crater lake near the top of Mt. Kusatsu-Shirane, is even more acidic (pH 1.0-1.2) and so there is little vegetation in the area. Yoshigadaira moor and Odaira moor provide an important refuge in the surrounding volcanic area for animal and plant species that depend on the wet environment.
The geothermal heat and water around the Yoshigadaira Wetlands enable wild fauna and flora to survive the winter at altitudes up to and beyond 2,000 metres and temperatures below -15°C. For example, the breeding site of the forest green tree frog Rhacophorus arboreus in Yoshigadaira Wetlands is at 2,150m, the highest recorded in the world.