The area of the Koubou-ike Pond was once a riverbed. During its time as a river, a big hole (pothole) was formed. After the river dried out, groundwater began to spring from the hole, and now the spring water is considered one of the 100 best waters in Japan. This kind of pothole, where groundwater springs in this manner, is rare in Japan.
Traditionally the hole was named after the famous Buddhist monk Koubou Daishi, who in return for the kindness of an elderly woman, is said to have struck a rock with his rod, causing water to gush out from the hole. A statue of the monk has been erected beside the hole. It is also called the Kama-ike Pond due to its resemblance to a 'kama' rice kettle.