The blue pond is in the altitude of about 500 meters in a position, and various expression is shown by the angle and the four seasons to see. This pond is that accumulated water in the dam was built in Bieigawa mainstream in order to prevent the volcanic mud flow disaster by Tokachidake of sediment that erupted in December 1988. That is, a blue pond is an artificial pond accidentally. As a result, trees which grew wild in the circumference, such as a larch and a white birch, sank and withered. The cause by which a pond looks blue is based on particulates such as aluminium hydroxide contained in the springwater of this neighborhood and sunlight.