It's the fine sediment, or rock flour, that creates the stunning blue colour in the water. The rock flour is light and stays suspended in the water where the light reflects off it creating the blue colour. A lot of lakes in the Canadian Rockies are glacial fed and this is why they can be so blue in colour.
The rock flour is formed during glacial migration, when glaciers move and grind against the rocks beneath them. The rock flour is then washed away into streams and lakes as the glacier melts.
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