Scientists Confirm World’s Largest Underground Thermal Lake Hidden 330 Feet Beneath Albania

Beneath the southern Albanian border with Greece, scientists have identified a massive thermal lake that now holds the title of the largest underground hot‑water reservoir documented on the planet. The lake, nestled inside the complex Atmos Cave system, is filled with warm, mineral‑rich water that has been sculpted by upward‑flowing geothermal fluids.

The first forays into the broader karst network occurred in 2021, when researchers probing the Vromoner thermal springs stumbled upon a series of subterranean passages. After several expeditions and extensive surveying, the Neuron Foundation confirmed the lake’s unprecedented dimensions.

Steam Column Pointed to a Hidden Abyss

Czech speleologists first noticed an unusual plume of vapor emerging from the limestone surface, hinting at a concealed water source beneath. This observation guided the team down a shaft that plunged more than 328 feet, where they encountered a vigorous inflow of thermal water feeding an expansive underground basin.

Expedition leader Marek Audy described the discovery in a statement issued by the Neuron Foundation:

“At its bottom, we discovered a strong thermal inflow and a vast lake,” adding that: “In order for Czech science to present this phenomenal discovery, it was necessary to conduct scientific research and precise measurements.”

According to the foundation, the lake lies roughly 330 feet below ground, while the accompanying scientific report places it at about 420 feet within Atmos Cave. Both measurements underscore the technical challenges involved in reaching the water body.

The lake, christened Lake Neuron in honor of the foundation that supplied key gear, was accessed using technical rope descents, continuous gas monitoring and advanced surveying instruments.

Laser Scans and Sonar Reveal Record‑Breaking Scale

Subsequent missions equipped the team with a mobile LiDAR scanner and sonar arrays, enabling a high‑resolution map of Atmos Cave and adjacent systems such as Sulfur, Breška and Kobyla. The data show Lake Neuron extending approximately 460 feet in length and 138 feet in width, with a shoreline totaling around 1,130 feet.

Surface area calculations approach 34,450 square feet, while depth measurements peak near 25 feet, translating to an estimated water volume of 294,300 cubic feet. Year‑round temperatures hover close to 79 °F, confirming the lake’s status as a persistent thermal reservoir.

These measurements cement Lake Neuron as the largest known underground thermal lake, a distinction that holds for all currently surveyed cave systems worldwide.

Geology, Chemistry and Ongoing Exploration

Atmos Cave’s formation is attributed to hypogene processes, where mineral‑laden hot waters ascend from depth rather than surface streams carving the passages. The Vromoner Valley’s geothermal fluids contain hydrogen sulfide; when this gas meets oxygen in the cave environment, it oxidizes into sulfuric acid, which slowly dissolves limestone and precipitates gypsum, eventually carving out large chambers such as the one housing Lake Neuron.

Tracer experiments indicate that the lake feeds several springs across the valley, though the Old Spa Spring appears to draw from a separate source. Combined spring discharge in the area measures roughly 53 gallons per second.

Research continues with multidisciplinary teams probing the region’s geology, hydrology and biology. Collaboration with local authorities aims to incorporate these hypogene caves into the expanding Vjosa National Park.

“It’s something that could have a huge impact on understanding underground ecosystems and geological processes,” said Audy. “We want to look at other parts of the cave, learn more about the geology and biology of this area.”

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