Tōshi Wetland is located in the Tōshi area of Nikaho City. There are many small hills scattered around this area, known as hummocks, and small reservoir ponds and wetlands in the depressions between them. This topography, along with the Kisakata area’s Kujūkushima Islands, was created by a debris avalanche that occurred here about 2,500 years ago, caused by the sector collapse of Mt. Chokai. Trees that were buried in the debris avalanche have been found near here.
The horseshoe-shaped depression on Mt. Chokai can be seen clearly from here.

Tōshi Wetland shows rich expressions in all four seasons with various flowers blooming, as well as other plants such as the Japanese alder tree (Alnus japonica). It was registered in 2001 by the Ministry of the Environment as one of the 500 Important Wetlands of Japan.
Every year in April, a controlled burn is held over an area of about 260 hectares (1 ha = 10,000 m²). The Japanese bracken fern (Pteridium aquilinum subsp. Japonicum) thrives here, and the edible aquatic plant watershield (Brasenia schreberi) can be harvested in one of the ponds found among the hummocks.