Silver birch trees

Silver birch trees in a blue pond, Furano, Hokkaido, Japan

Scientists aren’t entirely sure what causes the vibrant color in Hokkaido’s Blue Pond. The water itself isn’t unusual, and appears clear. But at different angles, times of day, and depending on the light and distance, the water of this small pond near Daisetsuzan National Park can look electric blue or turquoise. The current theory centers on the relatively high concentration of aluminum hydroxide in the sediment at the bottom of the pond, which can reflect light in short wavelengths of blue, just as Earth’s atmosphere does to make our sky blue.