Why does the Retba lake have the color of a carrot?

Mar 30, 2022 • 8:03 AM UTC

Almadies Arrondissement, Dakar, Senegal

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Microorganisms

Melanie Hannebelle

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The Retba Lake, also called Pink lake (“lac rose” in French) is a well-known water body in Senegal, near Dakar, the capital. The lake is astounding: it has such a bright, carrot-like color! I am also told that it is 10 time more salted than the ocean, and even more than the Dead Sea.

A lot of people are harvesting the salt from the lake bed, and after drying it in the sun, they get tons and tons of beautiful white salt.

Everybody on the boat is very excited to look with the Foldscope and see what is in the water. We observe a lot of round micro-organisms with a strong red color. They are so many, no need to concentrate the sample to have plenty to see on the glass slide. This explains why the water has such a bright color!

The micro-organisms are surprisingly sensitive to pressure, and a small force on the cover-slip makes they burst. We need to be careful while handling the Foldscope!
A little search on the internet tells us that these micro-organisms are in fact micro-algae named Dunaliella salina and are known to live in high-salt water bodies. And they contain contain a high amount of the same compound found in… carrots (beta-carotene). And now it makes sense why this lake has the color of carrots!