Lake Retba: The Pink Lake That Turned Green Overnight

Senegal's Lake Retba, known as Lac Rose, looks like a giant strawberry milkshake, its water so salty and pink you can float effortlessly. Then in 2022, the world-famous marvel lost its color almost overnight, turning a murky lifeless green. This episode explores the extreme biology behind the color, the thousands of people whose survival depends on its punishing waters, and the crisis that nearly erased it.We explain how seawater seeping through sand dunes into a basin with no outlet concentrates salt to ten times ocean levels, and how the alga Dunaliella salina produces red pigment to harvest sunlight for energy. We meet the salt collectors who coat themselves in shea butter to survive seven-hour shifts, the tilapia hiding in brackish pockets, and the flood of fresh water that diluted the lake and washed away nearly $700,000 of harvested salt.How evaporation in a blind basin pushes salinity to around 350 grams per literWhy the algae's red pigment is a survival mechanism, not just a stainHow harvesters use shea butter as a hydrophobic seal against the caustic waterThe lake's cultural footprint, from the Dakar Rally to a Michael Tippett compositionWhy a 2022 freshwater flood deactivated the algae and crippled the local economy