For years, people living near the Albanian-Greek border had no reason to suspect that there was a vast reserve of hot water hidden beneath the mountains surrounding them. The landscape gave only small hints. Steam started flowing from the cracks in the limestone. Mineral springs emerged in scattered places. However, beneath those signs, out of sight, existed an entirely different world. Far below the ground, in darkness untouched by daylight, a vast thermal lake lay isolated for an unknown period of time. Its existence became known when cave explorers unearthed clues hidden within the geology of the area and descended into a system that had never been properly mapped. What they found has been recognized as the largest underground thermal lake ever identified.
A hidden descent into the underground world of Albania
As reported by the Albanian Monitor Ekonomi magazine, the discovery is linked to exploratory work carried out by Czech speleologists examining the mountainous border area of southern Albania. His attention was drawn to the unusual geothermal activity seen on the surface. The hot springs and visible vapors suggested that a large source of hot water might be hidden somewhere beneath the limestone terrain.Tracking those signals, the team reached a deep vertical shaft. The opening descended approximately one hundred meters into a cave system that had not been previously documented. To reach the bottom the explorers required a controlled descent through a narrow chasm before emerging into a hidden chamber. There, beyond the reach of natural light, they found a large deposit of thermal water. At that time, it became immediately clear that the lake was important. What remained uncertain was its actual scale.
Scientists confirmed The world’s largest underground thermal lake
The first exploration provided only a rough understanding of the cave’s dimensions. The conditions inside the chamber made detailed measurements difficult. The lake was deep underground, access was limited and the surrounding air contained hydrogen sulphide, creating an environment that required caution. Early sketches suggest the lake may be exceptionally large, but confirmation will require more advanced equipment than was available at the start of the expedition. Several years passed before researchers were able to return with special scanning technology capable of making precise measurements inside the cave.When a larger expedition revisited the site, the results confirmed earlier suspicions. As reported by an Albanian magazine, the lake extends over 138 meters in length and almost 42 meters at its widest point. Calculations revealed that the volume of water exceeds 8,000 cubic metres, making it the largest underground thermal lake currently known.The measurements also revealed the scale of the chamber. The cave in the lake was much larger than initially anticipated, with sections extending beyond the areas examined during initial visits.
Why is this thermal lake unique from scientific point of view?
Its size alone would make the discovery remarkable, but the chemistry of the water adds another layer of scientific interest. The lake has a high concentration of hydrogen sulphide, a gas identified by its characteristic odour. In a closed environment, that gas can be dangerous. Within the cave, it has played a role in shaping the landscape for a very long time.Many cave systems form when mildly acidic rainwater slowly dissolves limestone. The Albanian chamber appears to have developed through a different process. As hydrogen sulfide rises and reacts with oxygen, sulfuric acid can form. Over time, that acid attacks the surrounding rock, changing it and enlarging underground spaces.The result is a cave environment that differs from many familiar karst systems. Chemical activity still continues, creating conditions that still shape the cave today.
What lives inside a hidden thermal lake?
It is completely dark inside the lake chamber. Sunlight does not reach water. Plants cannot survive there like they can on the surface, and the ecological rules are very different. Scientists believe the lake is likely inhabited by microorganisms that rely on chemical reactions rather than sunlight as their primary source of energy. Similar communities have been documented in other geothermal and sulfur-rich cave systems around the world, where bacteria thrive in conditions that would be hostile to many forms of life.Such environments often attract attention because they provide opportunities to study organisms adapted to extreme conditions. Researchers hope that future investigations will reveal whether there are microbial species in the lake that have not been described before.