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観光客の皆様へのおねがい A request to all visitors

Reason for blueness

This is the water of the Biei River and the water that contains sulfur and other hot spring elements such as sulfur contained in the tributaries that merge near Shirogane Onsen and “Shirohige no Taki” waterfalls, as well as aluminum. When these two waters mix, invisible “colloids” are formed. When sunlight collides with colloidal particles in water, light is scattered in various directions. It is said that blue light with shorter wavelengths is more easily scattered and thus reaches our eyes, making it appear blue. Another theory is that the white soil at the bottom of the pond reflects the light, enhancing the blue color. *The official name of the Blue Pond is “Shirogane Blue Pond.