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[Via the official GNP fbook page](https://www.facebook.com/media/set/?set=a.10150274356039912.335507.74553624911&type=1):
Glacial lakes and their outlet streams tend to have very low nutrient levels, a condition described scientifically as “oligotrophic.” The oligotrophic waters of the park are largely due to being located near the headwater source of the watersheds, local surface geology, lack of nutrient input from either human or natural sources, cold water temperatures, and short growing seasons.”
Which explains the low/lack of algae.
As to the coloration, it doesn’t translate well in this picture, but glacial lakes tend to look green (Wikipedia calls it turquoise), due to the aforementioned rock flour, which is derived from jasper.