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 Sea
, negotiations related to the demarcation of the Caspian Sea had been going on for nearly a decade among the states bordering the Caspian – Azerbaijan, Russia, Kazakhstan, Turkmenistan, and Iran. The status of the Caspian Sea is the key problem. Access to mineral resources (oil and natural gas), access for fishing, and access to international waters (through Russia's Volga river and the canals connecting it to the Black Sea and Baltic Sea) all depend upon the outcomes of negotiations. Access to the Volga River is particularly important for the landlocked states of Azerbaijan, Kazakhstan, and Turkmenistan. This concerns Russia, because the potential traffic would use its inland waterways. If a body of water is labelled as a sea, then there would be some precedents and international treaties obliging the granting of access permits to foreign vessels. If a body of water is labelled merely as a lake, then there are no such obligations. Environmental issues are also somewhat connected to the status and borders issue.