Although the Caspian Sea is endorheic, its main tributary, the Volga, is connected by important shipping canals with the Don River (and thus the Black Sea) and with the Baltic Sea, with branch canals to Northern Dvina and to the White Sea.Another Caspian tributary, the Kuma River, is connected by an irrigation canal with the Don basin as well.

Several scheduled ferry services (including train ferries) operate on the Caspian Sea, including:

a line between Türkmenbaşy, Turkmenistan (formerly Krasnovodsk) and Baku.
a line between Baku and Aktau.
several lines between cities in Iran and Russia.

The ferries are mostly used for cargo, only the Baku – Aktau and Baku – Türkmenbaşy routes accept passengers.

In short, the importance of Caspian Sea is for transportation.