Chlamydomonas nivalis is a unicellular red-coloured photosynthetic green alga that is found in the snowfields of the alps and polar regions all over the world. They are one of the main algae responsible for causing the phenomenon of watermelon snow (also blood snow, raspberry snow), where patches of snow appear red or pink. The first account of microbial communities that form red snow was made by Aristotle. Researchers have been active in studying this organism for over 100 years.