Not many people know the fact that the Caspian Sea is a salt lake, largest of the kind (374,000 km2, comparative with the area of Japan (377,835km2)).
The salinity of the lake differs in locations, lower in the northern area with the inflow of Volga River and higher in the southern area. The average salinity is approximately 1.2%, 1/3 of seawater.
The Caspian Sea is surrounded by Russia, Azerbaijan, Iran, Turkmenistan and Kazakhstan, and crude oil was spotted as early as 10th century. Further, the Capsian Sea is the crucial source of fishing for the region, and accounts for 25% of the Russian domestic fishing.
However, the Caspian Sea suffer from serious pollution due to the discharge of pollutants from oil field, refinery mills, sewage of inflowing rivers.