Final answer:
The Don River is the northern extension of the Black Sea and is connected to the Volga River through the Volga-Don Canal.
Step-by-step explanation:
The river that is the northern extension of the Black Sea and is connected to the Volga via a namesake canal is the Don River. The Volga-Don Canal links the Volga River, which flows into the Caspian Sea, with the Don River, providing a navigable waterway between the Caspian Sea and the Black Sea.
This canal is a crucial part of an extensive network of canals that facilitates transportation, migration of species, and industrial development in the region.