Why the Volga Empties into an Inland Lake: Geography of the Endorheic Caspian Basin

## The Mystery of Endorheic Sinks

Most continental rivers terminate in an ocean, bay, or marginal sea connected to the global water system. However, the **Volga River**—the longest waterway in Europe at 3,530 kilometers—drains into the **Caspian Sea**, a completely landlocked terminal saline lake sitting 28 meters below global sea level.

### What Is an Endorheic Basin?
An endorheic basin is a closed drainage catchment that retains water and allows no outflow to external bodies of water. Water that enters an endorheic basin can only leave via evaporation, seepage, or human consumption.

### The Water Balance of the Caspian Sea
The Volga contributes over **80% of all surface freshwater** entering the Caspian Sea. Because the lake has no ocean outlet, its surface level fluctuates entirely based on the mathematical balance between Volga river discharge and atmospheric evaporation. During hot dry decades, the Caspian recedes dramatically, exposing shallow shipping channels in the northern delta.