"The underwater giant: The river, shown with a 3D scan using false color, flows along the bed of the Black Sea" - The Daily Mail
The river is actually the continuation of the Bosphorus Strait as it pours water from the Mediterranean Sea into the Black Sea. The water from the Mediterranean is heavier because of its higher salt content and therefore sinks to the bottom. The force of the water digs into the soft Black Sea floor creating a river channel. The so far unnamed river is huge: up to 115 feet (35 meters) deep and half a mile (.8 kilometers) wide. This combined with the amount of water flowing through the river channel make the underwater river the sixth largest river in the world.
A neat thing to know about the underwater river is that it even has rapids and waterfalls! The ocean and seas are the world's last frontiers. Geographers who focus in oceanography are filling in the last "blank", actually blue, spots in the map. However, there is plenty of more spots to explore so if one wants to do on Earth discovers then oceanography may be up one's alley.
In 2009 I blogged about the below video in which the importance of oceanography and ocean exploration is discussed