Because we’re all surrounded by plants, we tend to have the association between photosynthesis and green things. While this is certainly true for most phototrophic life on Earth, it isn’t always the case. Every now and again, you find something which goes quite pointedly against our preconceptions. And this is one of them.
Lake Retba, also known in French as Lac Rose, is a salt lake in Senegal. The lake itself is coloured vividly pink by a type of cyanobacteria living in the lake, known as dunaliella salina. With a salt content much higher than the more famous Dead Sea, Lake Retba is one of the saltiest permanent bodies of water in the world.
These particular cyanobacteria are less cyan and more magenta, because of their remarkable adaptions for survival in such an unusual environment. A high concentration of β-carotene in their cell membranes helps them to survive the harsh African sun, and a similarly high concentration of glycerol enables them to survive the osmotic pressure of living within such highly saline conditions. Combined with the fact that very little else can live in this water, the bacteria thrive and give the lake its pretty pink hue. As you might expect, during the dry season, the water levels go down and make the bacteria more concentrated in the water – meaning that the water appears pinkest during the dryest times of the year.
Tip of the hat to Bangstyle!