The Caspian Depression is below sea level, consisting of large areas of marshlands in the eastern region.

It is one of the largest flat lowland areas in Central Asia, covering approximately 200,000 km2 (77,000 sq mi).

Some of them also believe that the North Caspian depression became separated from the open ocean in ancient times to form an enormous salt lake.

Russian satellite photos have revealed huge deposits of salt domes (about 1,200), in the Caspian Depression in western Kazakhstan.

The southern region of the depression, or the north coast of the Caspian Sea, is characterized by the large development of damp sites resulting from tidal phenomena.

Studies have shown that water pollution, mostly coming from the Volga River, poses a serious threat to the biodiversity of the Caspian Depression.