Lake Vouliagmeni ("Sunken Lake") is a small brackish-water lake fed by underground currents seeping through the mass of Mount

Hymettus Hymettus (), also Hymettos (; el, Υμηττός, translit=Ymittós, pronounced ), is a mountain range in the Athens area of Attica, East Central Greece. It is also colloquially known as ''Trellós'' (crazy) or ''Trellóvouno'' (crazy mountain) ...

located to the south of

Vouliagmeni Vouliagmeni ( el, Βουλιαγμένη, meaning "sunken") is a seaside suburb and former municipality 20 km south of Athens city centre. Since the 2011 local government reform it is part of the municipality Vari-Voula-Vouliagmeni, of which ...

Athens Athens ( ; el, Αθήνα, Athína ; grc, Ἀθῆναι, Athênai (pl.) ) is both the capital and largest city of Greece. With a population close to four million, it is also the seventh largest city in the European Union. Athens dominates ...

, Greece.

Description

The lagoon formed about 2,000 years ago. It was once a large cavern that collapsed following an earthquake. The outline of the collapsed cavern roof can be clearly discerned from a distance. The lake has quite unique environmental conditions: it is supplied with warm seawater (28-35°C) via an underground channel spreading through a network of flooded caves, so its temperature never drops below 18 °C (usually ranges around 21-24 °C), whereas a freshwater spring reduces its salinity to brackish levels (14.5-18 psu). It continues deep inside the mountain in an underwater cave never fully explored, as its end seems impossible to trace even by employing sonar detection. Many underwater expeditions have been carried out in order to chart it, and a few amateur divers have drowned trying. Because of its constant warm water temperature and its rich content in

hydrogen sulphide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The unde ...

, the lake functions as a

spa A spa is a location where mineral-rich spring water (and sometimes seawater) is used to give medicinal baths. Spa towns or spa resorts (including hot springs resorts) typically offer various health treatments, which are also known as balneoth ...

since the end of the 19th century.

Ecology

The lake hosts the only existing population of a species of sea anemone, '' Paranemonia vouliagmeniensis''. It has been declared a natural monument by the Greek State and is part of a

Natura 2000 Natura 2000 is a network of nature protection areas in the territory of the European Union. It is made up of Special Areas of Conservation and Special Protection Areas designated under the Habitats Directive and the Birds Directive, respectively ...

References

{{Reflist Geography of Attica

Natura 2000 in Greece