The Seine rises on the Langres Plateau and flows northwest into the English Channel. The river is 776 kilometres (482 miles) long. It is navigable for riverboats from Bar-sur-Seine, which is more than 560 kilometres (350 miles) from its mouth, and for ocean shipping from Rouen, which is about 121 kilometres (75 miles) from its mouth.

The Seine has many tributaries including the Aube, Marne, and Oise rivers from the north and the Yonne and Eure rivers from the south. It is connected by canal to Schelde, Meuse, Rhine, Saône, and Loire rivers. In January 1910 disastrous floods occurred in Paris as the river rose to more than 7 metres (24 feet) above its normal level.