What is Watermelon Snow?

Mary McMahon
Mary McMahon

Watermelon snow is snow which has become discolored due to the presence of cold-loving algae, specifically Chlamydomonas nivalis, an alga with a distinctive pink to red color. When this organism colonizes a section of snow, the snow appears pinkish to red, depending on how compressed it is, and it even has a faint watermelon scent. Watermelon snow tends to appear at high altitude, and it can be found all over the world, including regions where snow appears seasonally, rather than year-round.

Watermelon snow tends to appear at high altitudes, such as mountain tops that may receive snow seasonally or year round.
Watermelon snow tends to appear at high altitudes, such as mountain tops that may receive snow seasonally or year round.

People have been noticing watermelon snow for thousands of years. The Ancient Greeks, for example, puzzled over the phenomenon, as did 19th century explorers in the New World, who concluded that the strange red color was due to the presence of iron. Only with the assistance of microscopes did people realized that watermelon snow was caused by a living microorganism. The existence of cold-loving algae also suggested that other extremophilic organisms might someday be discovered, and this proved to be the case, illustrating that life will thrive just about anywhere, if given a chance to do so.

Microscopes helped scientists discover that watermelon snow was caused by a living organism.
Microscopes helped scientists discover that watermelon snow was caused by a living organism.

The red color isn't just for looks. The carotenoid pigment which turns the algae pink helps to insulate it from the cold, and to protect it from harmful UV radiation. The evidence seems to suggest that the algae actually colonizes the ground, and when it becomes covered with snow, it slowly works its way to the surface, creating streaks, pits, and patches of reddish color in the snow. Watermelon snow can sometimes extend across a very large area, creating a very striking sight.

When people walk on watermelon snow, they compress the algae, resulting in a deeper red color. They also pick up the color on their shoes and pantlegs, leaving a trail of pink footprints in the snow until all of the algae has been scuffed off their garments and shoes. Since watermelon snow is so visually distinctive, it often becomes a topic of conversation on hikes, not least because it looks like the ghoulish remains of a climbing accident.

Technically, watermelon snow is edible. However, snow can easily be contaminated with bacteria and algae which are not safe to eat, and eating large quantities of watermelon snow can lead to intestinal distress. Therefore, eating this discolored snow is not recommended, although people interested in the science might want to collect a small sample to examine under a microscope at home. Magnified, the algae which causes the peculiar red color is actually quite pretty.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


I tasted it when I was in Mount Lasson. It tasted a bit like watermelon.


@chivebasil - Did your father say what the watermelon snow tasted like? I'm curious to know if the actual taste had any resemblance to watermelon, given the similarity in smell.


@turquoise - In Quebec too there is a tradition of pouring hot maple syrup over snow and then eating it when it has cooled down. As the article mentions however, large amounts of watermelon snow can cause digestive illness, so it's definitely not recommended!


@alisha - You're right; I think the natural reaction for many people is to fear things that are strange or unknown to them. In the case of watermelon snow, it certainly looks alarming to those who don't know the true cause of it. I wonder if people in the old times would have believed it if they were told that the snow was red only because of algae!


I read that when the British expedition ships came back and mentioned watermelon snow that they had seen in Greenland in the 1800s, everyone thought that the snow fall in Greenland was naturally red. People had lots of different ideas about why it was red but then scientists found out about the algae.

It's so funny how our imagination runs wild when we don't know what we are dealing with. I think I would have thought the same way if I lived in that time period. I would have probably thought that it was blood, or maybe even some sort of divine sign.

Thank goodness we have enough scientific knowledge and tools to find out the real causes of things.


I saw watermelon snow once in Colorado. I was pretty shocked at first. I actually thought we might have come across a crime scene or something. The color is not that deep of a red but I was young and the mind wanders to weird places sometimes.

My dad explained what it was and he actually stooped down to eat some. He seemed to like it but no one else in my family would try it.


@turquoise-- No, it's not tempting at all. It doesn't have a uniform red color. I've seen watermelon snow a couple of times in California. It was just in some places (not like hills of red snow) and in small streaks like someone spilled their fruit punch.

I don't know, I sure wasn't tempted to try it. The scent is interesting, maybe reminiscent of watermelon but not exactly. You should look up pictures of watermelon snow, you'll know what I mean better then.


I wonder if anyone has actually eaten this snow because it looks like snow cones and smells like watermelon? I think I would be willing to try it.

My family is from Kashmir and my mom told me that they actually sold snow sweets in Kashmir in the summer time. They would bring down clean snow from the mountains and pour sweet fruity syrups on top to basically make a snow cone. The snow was also used to keep foods cool because refrigerators weren't common then.

So I guess if it is clean, snow could be eaten but probably not watermelon snow. I bet the algae would cause a stomach upset.

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