Caspian Sea
The Caspian has characteristics common to both seas and lakes. It is often listed as the world's largest lake, although it is not a freshwater lake. It contains about 3.5 times more water, by volume, than all five of North America's Great Lakes combined. The Caspian was once part of the Tethys Ocean, but became landlocked about 5.5 million years ago due to plate tectonics. The Volga River (about 80% of the inflow) and the Ural River discharge into the Caspian Sea, but it has no natural outflow other than by evaporation. Thus the Caspian ecosystem is a closed basin, with its own sea level history that is independent of the eustatic level of the world's oceans.
Buzachi Peninsula
This peninsula is a vast low-lying depression with salt marshes and salt lakes. Parts of it lie between 20 and 30 m below sea level, lower than the Caspian. The area provides an important habitat for thousands of Goitered Gazelles.
The area was mapped by Fedor Ivanovich Soimonov during the Caspian Expedition, which surveyed the Caspian Sea from 1719 to 1727.