Where in France is the seine river located?

Well, it starts in the English Channel and goes through Paris, Rouen, and Troyes. It ends near Dijon.

No it doesn't.
The source of the River Seine is at Sainte-Seine-L'Abbaye in the Côte d'Or, it flows down through Troyes, Melun, Paris, Rouen and flows into the Atlantic Ocean at Le Havre
http://fr.wikipedia.org/wiki/Seine