Caspian Sea - 371,000 Square Kilometers

The Caspian Sea has characteristics common to both seas and lakes and is listed as the world's largest lake, although it is not a freshwater lake. It is the world's largest enclosed inland water body, with a total surface area of 371,000 km², holding 78,200 cubic km of water by volume which is about 3.5 times more water by volume than all five of the Great Lakes combined. Besides this, it is also the 3rd-deepest lake in the-world. The Deepest part of the lake is 1,025 m, and the lake has a length of 1,199 km at its longest span, with an average depth of 211 m. The Caspian Sea is unique as the only Oceanic Lake on this list, with the rest being considered as Continental Lakes. This is because rather than being entirely over the continental crust, the Caspian Sea has an Oceanic Basin. It also is an “endorheic basin”, referring to it being a closed system with no outflows. The Caspian Sea has Iran, Kazakhstan, Turkmenistan, Russia and Azerbaijan among its basin countries. The Volga, Ural, Terek, and Kura Rivers all serve as major sources of inflow feeding the Caspian Sea.

source by http://www.worldatlas.com/articles/10-largest-lakes-in-the-world.html