Kootenay River, Kootenay National Park, British Columbia, Canada

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Why is the Kootenay River so blue? I don't have a definitive answer, but it seems to be three factors, typical of rivers in the high Canadian Rockies.

1. There is little sediment or chemical leaching from the hard Precambrian rocks that comprise the Canadian Rockies
2. The water hasn't filtered through much forest on its way off the peaks, therefore gaining little sediment or dissolved tannins
3. Colloidal calcium carbonate (CaCO3) in the water has optical properties that enhance the tendency of deeper water to reflect a blue / cyan / turquoise color.

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