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.
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.