The Blue Pond is a ‘check dam,’ made of concrete to protect the Biei River against damage from volcanic mudflows. Water accumulates from upstream, flowing into the pond itself.

Trees such as the white birch, and larch, which once grew on the dry riverbed, have withered due to being submerged in water.

The water of The Blue Pond appears to be blue.

The Biei River starts near the Shirogane Hot Spring area, where rivers such as the Shirinashizawa River and Iwozawa River, which flow down from Mt. Tokachidake, merge to form it.

Within this water flowing out of the volcano are extremely small particles of aluminum silicate (approximately 1/10,000 to 1/1,000,000 of a millimeter) These particles flow into the Blue Pond.

These particles absorb red light, and produce blue light, through a phenomenon known as 'scattering.' This blue light is what gives the Biei River its blue appearance.