‘Watermelon snow’ graces Yosemite in August — but don’t taste it, rangers warn

Trying to satisfy a watermelon craving? Stick with the real thing.

The so-called “watermelon snow” on the ground in August at Yosemite National Park won’t taste fruity — because it’s pigment being released by a cold-weather algae, which thrives at high elevations in the California park as snow melts and leaves freezing water where algae blooms, rangers explained in a Facebook post that has been shared hundreds of times.

The algae, called Chlamydomonas nivalis, does well in parts of the park above 9,500 feet, where snow sticks around and melts well into the summer months, rangers said.

“This algae is typically green but contains a special red pigment called a carotenoid that acts as a protective barrier, shielding the algae’s chlorophyll,” rangers explained, sharing photos of the chemistry in action. “Since chlorophyll is necessary for its survival, it uses this natural type of sunscreen to protect itself from too much heat and damaging UV radiation.”

Rangers added that the “pigment dyes the surrounding area a darker color, giving the effect of a pink or red snow field, and allows the snow to heat up faster and melt more quickly.”

It’s a phenomenon humans may be familiar with.

“Imagine wearing black instead of a white T-shirt in the sun. It feels much hotter,” said Stefanie Lutz, a geobiologist at GFZ German Research Center for Geosciences, according to the New York Times. “It is the same for the snow: More heat means more melting.”

Lutz and a team of other researchers published a study in 2016 that said climate models should consider the impacts of “watermelon snow” — with Lutz fearing a “runaway effect” in the future where global warming melts snow and triggers algae growth, which then darkens snow and causes even more melting and more algae growth, the Times reported.

One Facebook commenter this week asked the inevitable about the snow.

“So don’t eat the pink snow?” she wrote on Monday.

“Exactly,” park rangers responded.

That’s not to say people haven’t learned the hard way.

“Oddly enough, it’s even said to smell a bit like watermelon. So why shouldn’t you find out if it tastes that way too?” Jennifer Frazer writes for Scientific American. “According to botanist Joyce Gellhorn’s 2002 book ‘Song of the Alpine,’ there’s a very good reason: in addition to being tantalizingly refreshing-looking on a hot day after a long hike where a snow cone would be just the ticket, it’s also a laxative.”

Still, risking a taste might be fine.

“Although it probably isn’t harmful to eat, we certainly don’t recommend it,” said park spokesman Scott Gediman, according to TODAY. “All snow (watermelon or not) should be treated before consuming,”

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Jared Gilmour is a McClatchy national reporter based in San Francisco. He covers everything from health and science to politics and crime. He studied journalism at Northwestern University and grew up in North Dakota.