Rivers draining the glaciated high country, including the Hoh, often appear a milky gray-blue. The tint comes from glacial flour, rock pulverized so finely by moving ice that the particles remain suspended in the water rather than sinking, coloring the flow from the high peaks all the way to the Pacific.
Cross a river along here and look at the color of the water. Some of these rivers run milky, a pale slate blue, almost like watered-down paint. That's glacial flour. High up, the glaciers grind bedrock into a powder so fine it never settles out, and it stays suspended all the way down to the sea, tinting the whole river that cloudy gray-blue. So that strange color isn't pollution. It's a mountain being slowly turned to dust and carried past you.
Photo: Olympic National Park (U.S. National Park Service) · Public Domain
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