The swimming hole was discovered by shepherds about three weeks ago when they stumbled across the huge beautiful blue coloured lake. But three weeks on, it is green with algae and subject to public health warnings.Despite the mystery surrounding how 'Gafsa Beach' suddenly appeared in the area, and what effect, if any, the local phosphate mining industry might have on the water quality, the huge pool has provided much needed respite for locals where temperatures are reaching 40C.There has been no explanation given for how the lake came to be, but some have suggested seismic activity caused groundwater to rise to the surface.Journalist Lakhdar Souid told France 24: 'News of the lake’s appearance has spread like wildfire and now hundreds of people, eager to escape a heatwave, go there to swim.'The region was 'overflowing' with large deposits of phosphate, which can leave behind radioactive residue, he said.'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.'Gafsa’s Office of Public Safety has issued a public warning the lake is dangerous and unfit for swimming - but that has not stopped locals from using it as their local swimming pool.The Guardian reported Mehdi Bilel spotted the lake after several hours on the road.'After several long hours on the road without a break, I honestly thought I was hallucinating. I don't know much about science and thought it was magic, something supernatural.'Bathers have now set up a Facebook page to document their activities at the mysterious lake, while local authorities continue to conduct tests to establish whether or not it is safe to swim in.(dailymail.co.uk)Bakudaily.az