For the past three weeks, hundreds of swimmers have been flocking to a lake in the Gafsa region of southern Tunisia. But the sudden, mysterious appearance of this lake in a drought-hit area has raised concerns about both the origin and the quality of the water.

Locals discovered this mysterious lake alongside Om Larayes road, about 25 kilometres from Gafsa. Local authorities say the lake’s total volume is about one million square metres spread over a surface of about one hectare. The lake’s depth ranges from about 10 to 18 metres.

Last Monday, two weeks after the site was discovered, Gafsa’s Office of Public Safety warned that the lake was dangerous and unfit for swimming.

When interviewed by FRANCE 24, Public Safety director Hatef Ouigi said this warning was a cautionary measure undertaken while teams of experts verified the water’s quality. The results of the tests would determine any future action taken by the authorities.

Despite potential risks, locals crowded the banks of the lake last weekend, as evidenced by photos posted on Facebook.

Photos and videos were posted on the Facebook page "Lac de Gafsa".

"There’s a real risk that the water is contaminated and carcinogenic”

Lakhdar Souid in a journalist from the Gafsa region. For the past few days, he has been conducting an investigation into the origin of the lake as well as the potential health risks for swimmers.

Local shepherds discovered this vast expanse of water about three weeks ago. News of the lake’s appearance has spread like wildfire and now hundreds of people, eager to escape a heatwave, go there to swim. They have christened it “Gafsa Beach.” Many people are calling the lake’s appearance a miracle.

So far, local authorities have provided no explanation for the lake’s sudden appearance. That’s why I contacted a geologist working at Gafsa’s college of science who had come up with a number of theories about the lake’s origins, one being that seismic activity upset the water table, causing groundwater to rise to the surface.

For the time being, the origins of this lake remains a mystery, but our biggest concern right now is the quality of the water. This region is overflowing with large deposits of phosphate, which can leave behind radioactive residue [Editor’s Note: The city of Gafsa is located in a valley in the eponymous mountain range. Phosphate mining is the region’s main industry.]

So, there is a real risk that this water is contaminated and carcinogenic. On the first few days, the water was a clear, turquoise blue. Now, it is greenish and filled with algae, sure signs that the water is stagnant, which means it’s a perfect breeding ground for parasites and disease.

Last Friday, despite the warnings issued by the Office of Public Safety, hundreds of swimmers came to the lake. The site is certainly stunning and there are many large rocks perfect for diving. So to truly dissuade people from coming, we’ll need something more convincing than a little warning.

Post written with FRANCE 24 journalist Grégoire Remund (