Streaks of red and patches of pink are not a sight I was expecting to see way up in the mountains. Out there, without the city’s foot and car traffic turning the pretty white fluff into brown slush, I assumed the snow would stay white until it melted in the heat of summer.

But as we hiked up a snow filled basin, squinting against the blinding sun, I knew I wasn’t seeing things. There it was again: bright pink dips and streaks in the snows surface!

When I researched it, I found it has many names: watermelon snow, snow algae, blood snow. Initially, explorers thought it was iron mineral deposits, but now we know it’s alive.

photoSylvia Dekker

Microscopic and photosynthetic, Chlamydomonas nivalis is a freshwater green alga found in alpine and polar environments globally. It loves cold temperatures and contains a high concentration of carotenoids, the same type of vivid red pigment that colours tomatoes and maple leaves red in the fall. The same explosions of algae populations that threaten the health of lakes and oceans, better known as algal blooms, results in swathes of rosy colour on the snow’s surface. It’ll stain your clothes pink or red too: check your pant cuffs after stomping through a drift of it!

The alga lies dormant in the winter between the layers of snow, and once spring starts to transform the algae’s preferred elevations of 10,000 to 12,000 feet, the cells germinate and swim to the surface of the snow pack. There, in the bright sun, the pigment is activated and works as a sunscreen. The alga feed on micronutrients, rock and soil minerals, and tree pollen, and are dispersed to all the far-flung places we like to explore by those whipping mountain winds. Once nutrients are in short supply, tough cells are created and will lie dormant, buried by drifts of snow during the winter, until the following spring.

photoSylvia Dekker

Watermelon snow is the perfect name: not only is it pink, but some say it even smells like our favourite summertime fruit. Be aware, though, that no matter how delicious it may look and smell, snow algae can function as a laxative and cause digestive upset. While consuming tiny amounts is not known to be harmful, eating a lot can cause diarrhea, an uncomfortable and potentially serious ailment when out in the mountains.

A variety of animals such as protozoans, snow worms and spring tails, however, love to snack on the algae. In turn, these tiny living things feed spiders and insects, which become food for mountain birds.

Chlamydomonas nivalis blooms are fascinating and have a place in the ecosystem, but candy cane-striped snow has a downside too. Bright white snow reflects a lot of the sun’s warming energy. When covered with bright red pigment, heat absorption skyrockets. In fact, the pink tinge can reduce reflection by up to 13 per cent. The result: accelerated melting of snowbanks and glaciers.

Any addition of colour to the snow, whether it’s ash, dirt or algae, will affect the rate of melting. There are other organisms that tint snow and ice too. For example, certain bacteria dye Greenland’s ice sheets purple, brown or gray.

Watermelon snow algae tends to collect in sun cups, those rounded, puddle like indentations in the snow’s surface. The more concentrated the algae, the darker the colour and the faster the snow melts.

Luckily, you can still find pristine areas of white snow during the summer, and not every patch is tinged pink.

photoSylvia Dekker

Have you ever seen watermelon snow on your travels through the mountains?