The pink colour comes from tiny living things in the water - a kind of algae called Dunaliella salina. These algae love very salty water, and they make a red colour to protect themselves from the strong sunshine, a bit like sun cream. When millions of them all sit just below the surface, the whole lake turns pink.
Lake Retba is one of the saltiest places on Earth. It is about ten times saltier than the sea, and almost as salty as the famous Dead Sea. The water is so salty that you can lie on your back and float without trying - the salt pushes you up like a cushion.
Hundreds of workers harvest salt from the lake by hand. They stand in the shallow water in long wooden boats, scooping salt off the bottom with baskets. They rub shea butter on their skin to protect it from the strong salt. The harvested salt is piled into bright white hills along the shore - pink lake, white hills, blue sky.
The lake is small - only about 3 square kilometres - but it is one of the most photographed places in West Africa. It changes colour through the day, from light rose in the morning to deep pink at midday. After a big rain, it can fade to almost grey for a while before brightening up again.