Rybinsk Reservoir , informally called the Rybinsk Sea, is a water reservoir on the Volga River and its tributaries Sheksna and Mologa, formed by Rybinsk Hydroelectric Station dam, located on the territories of Tver, Vologda, and Yaroslavl Oblasts. At the time of its construction, it was the largest man-made body of water on Earth. It is the northernmost point of the Volga. The Volga-Baltic Waterway starts from there. The principal ports are Cherepovets in Vologda Oblast and Vesyegonsk in Tver Oblast.