What Makes the Vivid Colors in Mountain Lakes?

One of the joys of hiking in Washington is the stunning beauty of our alpine lakes. If you’ve hiked to many mountain lakes, you’ve likely noticed that many of them are particularly blue — some almost seem otherworldly in their intensity. But what makes those lakes such an eye-popping color? Well, a lot of it has to do with what’s in the water — and what isn’t. Here’s the basics. 

The bright blue Lyman Lakes from atop Cloudy Peak. Photo by James Benthuysen.

Clear blue water

For lakes that are crystal clear, transitioning to vivid deep blues, the color can mostly be attributed to what’s not in the water. In this case, not a lot of silt or biological material. These clear lakes are often at higher elevations or in very cold areas. These lakes have fewer nutrients and a shorter growing season, so they don’t get as much algae or other biological material growing in them. That means that the water tends to be clearer. 

• Take care
• Mountain lakes are beautiful but also delicate. To help protect them, be careful to avoid adding any contaminants to them. For instance, don’t swim after applying bug spray and don’t do dishes in or near a lake.

To understand why those lakes appear blue, it helps to understand that light travels in waves and that different colors of light have different wave lengths. At one end of the spectrum, we have red and orange, with relatively long wave lengths. At the other end of the spectrum, we have blue and violet, with shorter wave lengths. When light hits the water, most of the longer wave lengths — red, orange and yellow in particular — are absorbed. But the blue color range is not absorbed, meaning that after it passes through a depth of water, the blue color is what you see. And without any sort of debris in the water, you get a clear, vivid blue.    

Also, if you look at a clear lake, you’ll probably notice that the blue color gets darker and deeper as the actual depth of the water gets deeper. That’s because it’s passing through more water and you’re not seeing any color from the lake bottom. 

Turquoise waters at Blanca Lake. Photo by Jessi Loerch.

Turquoise water

Some lakes have a color so spectacular and unexpected it seems Photoshopped. Think of lakes like Diablo Lake, Blanca Lake and Lyman Lakes. Those lake appear a milky turquoise color that can shift more blue or green depending on the lighting and other factors. The color in those lakes is caused by something called glacial flour. The lakes are fed by water that runs off of glaciers, and that water carries with it fine particles of rock that have been ground up by the massive weight of the glaciers. (Think of a glacier acting like sandpaper over the underlying rocks.) 

When that flour ends up in the water, it’s so fine it stays suspended. This glacial flour affects how the sunlight is absorbed — mostly absorbing the purple/blue colors of the spectrum. And because the water is absorbing the reds, oranges and yellows, what you end up seeing is mostly green with some blue — hence the spectacular colors.