Watermelon snow also called snow algae red snow or blood snow is Chlamydomonas nivalis a species of green algae containing a secondary red carotenoid pigment (astaxanthin) in addition to chlorophyll. Unlike most species of fresh water algae it is cryophilic (cold loving) and thrives in freezing water. Its specific epithet nivalis is from Latin and refers to snow.
This type of snow is common during the summer in alpine and coastal polar regions worldwide such as the Sierra Nevada of California. Here at altitudes of 10 000 to 12 000 feet (3 000