Largest lake ever
Megalake Paratethys
2,800,000 square kilometre(s)
Not Applicable (Eurasia)

Forming c. 12 million years ago, the largest lake ever known to have existed on Earth is Megalake Paratethys, which extended from the eastern Alps of Europe to what is now Kazakhstan in central Asia. At its peak, c. 10 million years ago, it’s estimated to have covered an area of 2.8 million square kilometres (1.08 million square miles) – making it slightly bigger than the modern-day Mediterranean Sea – and held a volume of more than 1.77 million cubic kilometres (424,645 cubic miles) of brackish water. The lake’s proportions were calculated in a study published in the journal Scientific Reports on 1 June 2021.

The scientists used a range of methods to estimate the size of the former megalake, primarily collating extensive paleogeographic data to produce digital elevation models (DEMs) that provided 3D maps of the lake’s bathymetry. Historical tectonic activity in the region was taken into account when determining the lake’s dimensions, as were fossil finds, sediment deposits and rock types across the Eurasia region.

Over its 5-million-year lifetime, a combination of climate change and tectonic activity dramatically reduced the size of Megalake Paratethys. During the most intense period of desiccation, between 7.65 and 7.9 million years ago, it lost more than one-third of its water and around two-thirds of its surface area, dropping by about 250 m (820 ft). A later refilling of the lake is thought to have caused an overspill into the Mediterranean Sea between 6.7 and 6.9 million years ago, spelling the lake's final demise as it was no longer a discrete body of water.

The Black Sea, Caspian Sea and Aral Sea, once basins in the bed of the Paratethys, are now the main remnants of the megalake.

The Paratethys once played host to a variety of endemic fauna found nowhere else on the planet, including Cetotherium riabinini, the smallest baleen whale in the fossil record, reaching lengths of around 3 m (9 ft 10 in).

The study was a collaboration between Utrecht University (Netherlands), the University of São Paulo (Brazil), the Russian Academy of Science (Russia), the Senckenberg Biodiversity and Climate Research Centre (Germany) and the University of Bucharest (Romania), led by paleo-oceanographer Dr Dan Palcu of the University of São Paulo.