Caspian Sea
The Caspian Sea, like the Black Sea, Namak Lake, and Lake Urmia, is a remnant of the ancient Paratethys Sea. It became landlocked about 5.5 million years ago due to tectonic uplift and a fall in sea level. During warm and dry climatic periods, the landlocked sea almost dried up, depositing evaporitic sediments like halite that were covered by wind-blown deposits and were sealed off as an evaporite sink when cool, wet climates refilled the basin. (Comparable evaporite beds underlie the Mediterranean.) Due to the current inflow of fresh water, the Caspian Sea is a freshwater lake in its northern portions, and is most saline on the Iranian shore, where the catchment basin contributes little flow. Currently, the mean salinity of the Caspian is one third that of Earth's oceans. The Garabogazköl embayment, which dried up when water flow from the main body of the Caspian was blocked in the 1980s but has since been restored, routinely exceeds oceanic salinity by a factor of 10.
Caspian lamprey
The Caspian lamprey is an anadromous fish which spends its adult life in the Caspian Sea and migrates up the Volga, Sura, and other rivers to spawn. It was at one time a common fish caught in nets and fish traps in the lower Volga for extracting fish oil and making candles and later for human consumption. In the early 1900s, 15 to 30 million fish were harvested annually from the lower Volga. It is now an uncommon fish because its migratory routes have been disrupted by dams and construction projects and it can no longer reach its spawning grounds.