Natural Wonders: Lac de Gafsa

In 2014, a miracle occurred in southwestern Tunisia. It was a time of extreme drought, and three shepherds were in the desert, trying to withstand the 40°C heat. They stopped in their tracks when they stumbled upon an almost impossible sight: a beautiful turquoise lake that had seemingly appeared overnight. Regarding its beauty, however, looks can be deceiving. More on this later.

Naturally, word of this miraculous lake spread to nearby towns, prompting locals to explore it for themselves. The refreshing waters were a gift from the intense sun and dust. Visitors did not hesitate to swim or dive from high ledges.

It came at the perfect time, when people needed it most. They called it Lac de Gafsa, because it was only 25km from Gafsa, the capital city of that region. Not surprisingly, the oasis experienced quite an upswing in tourism. A Facebook group was created to post photos and spread the good news: one of the good uses of Facebook, arguably.

Jumping into the lake. Photo: Anis Jaballah/Lac de Gafsa Facebook Group


The lake is one hectare wide and believed to be about 20m deep, though no one has checked. Since its discovery, there have been no official reports or studies done on the lake. Its origin remains a mystery.

There are two main theories, which have yet to be proven. Since Tunisia is prone to moderate earthquakes, the more popular theory is that an earthquake split the rock above the water table. This allowed water to rise to the surface and flood the area. The second theory is that the lake is a collection of rainwater. This is less probable because it would have taken many years and a lot of rain to get to this size. Someone would have come across it sooner or later. 

Behind the beauty, danger

What alerted authorities of the lake’s potential danger was its change in color. Within weeks of its discovery, the waters shifted from blue to mucky green. The lake suddenly had an algae bloom.

Authorities tried to dissuade visitors from swimming, but a lake in a desert is a tempting place on a hot afternoon, and crowds still flock to the little beach. There are no security measures to keep people away.

Since the late 1800s, Gafsa has mined phosphate and extracted millions of tonnes of raw material every year. Production fell during the revolution in 2011, but the surrounding soil remains rich in residual phosphate. It is highly likely that the water is also radioactive. 

Green algae on the water surface from phosphate pollution. Photo: SergeyYrev/Shutterstock


Too much phosphorus is capable of great harm. Phosphorus (particularly the white variety) is used to produce weapons like bombs, ammunition, explosives, fertilizers, and rat poison. High levels of phosphorus can lead to algae blooms. This eventually leads to eutrophication, the process in which oxygen levels decrease. This kills any aquatic life and makes humans sick from algal toxins in the bloom.

Phosphorus also has radioactive properties, which can lead to skin ailments, and kidney, liver, and heart problems. Lakes and ponds with high levels of phosphorus are called “dead zones”. There are many other examples of this phenomenon such as Chao Lake in China and Chesapeake Bay near Washington, D.C. in the U.S. 

Meanwhile, the mystery of the lake’s formation remains a puzzle.