What Makes Mountain Lakes So Blue?

Island Lake, one of the lakes you’ll encounter on the Ice Lakes Basin Trail. Photo Credit: SumikoPhoto (iStock).

If you’ve ever done a high- alpine hike during the summer months in Colorado, there’s a good chance you’ve come across a lake or pond. While these lakes might not be as massive as their lower altitude relatives, they are often filled with bluer waters than what you’ll find anywhere else. The water can even seem unnatural at times, as if someone filled it with food dye because of its intense turquoise blue hue. This begs the question: what makes these mountain lakes so blue?

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The first guess most people have is that it’s a reflection of the sky through the purest and most pristine waters around. After all, mountain lakes are often in such remote areas that they aren’t polluted like heavily trafficked bodies of water. While there’s no doubt these lakes might be less disturbed, it’s far from the truth to assume that sky’s reflection is more vibrant in these waters.

What Makes Mountain Lakes So Blue?

Blue Lakes in Colorado’s San Juan Wilderness.

In fact, these lakes are so blue because of the presence of something floating in the water. As the warmer months hit, glaciers melt, thus filling these pools with their water. With this glacial melt comes something called glacial flour. It’s basically finely ground rock. Unlike other objects that make their way into the lake water, this glacial flour is so light that it doesn’t sink. Instead, it stays suspended in the liquid, most clearly visible near the surface. These particles distort the wavelengths of lights that hit the lake, reflecting visible hues that fall in the blueish-green end of the spectrum.

So there you have it. The blue of a mountain lake isn’t because the mountain lake is filled with the purest water around. On the contrary, it’s actually the presence of something floating in the water that distorts the color we end up seeing.

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