In western Canada, several rivers and lakes turn a striking milky turquoise each summer, especially in regions near the Rocky Mountains. This unusual colour appears only when nearby glaciers begin melting and shifting. The key ingredient behind the glow is glacial rock flour—extremely fine particles created when glaciers grind against bedrock.
As a glacier moves, its enormous weight scrapes and crushes rocks beneath it into powder as fine as talcum dust. During warmer months, melting water washes this powder into rivers. The particles are so tiny that they do not settle at the bottom. Instead, they stay suspended in the water, giving it a cloudy, glowing appearance.
The turquoise colour itself is the result of sunlight. When light enters water filled with glacial flour, red wavelengths are absorbed more strongly while blue and green wavelengths scatter back toward the viewer. This scattering makes the water appear bright turquoise, especially on sunny days. On cloudy days or when the glacier is not actively melting, the river looks far less colourful.
The glow is temporary. In spring and early summer, glaciers melt rapidly, releasing more rock flour than at any other time of the year. As temperatures drop or melting slows, fewer particles enter the river, and the water gradually returns to a clearer tone. Because each river receives a different amount of glacial powder, no two waterways look exactly alike.
This phenomenon is most visible around places like the Kicking Horse River, the Bow River, and the waters feeding into Lake Louise and Peyto Lake. The changing colour is a natural signal of how active the glacier has been that season.
Light scattering
Blue and green wavelengths reflect strongly in glacial rivers.
Seasonal change
Turquoise colour peaks during warm months of rapid melt.
Rocky Mountain flow
Several Canadian rivers are fed directly by glacier meltwater.