Couesnon

The Couesnon is a river running from the département of Mayenne in north-western France, forming an estuary at Mont-Saint-Michel. It is 97.8 km (60.8 mi) long, and its drainage basin is 1,124 km2 (434 sq mi). Its final stretch forms the border between the historical duchies of Normandy and Brittany. Its historically irregular course, shifting between two beds to the north and south of Mont-Saint-Michel until eventually settling on the southern one, inspired the saying Le Couesnon en sa folie mit le Mont en Normandie (“The Couesnon in its madness placed the Mont in Normandy") as the Mont is just to the Norman side of the river’s current mouth. However, the modern administrative boundary separating the two regions does not follow the river course; it is some six kilometres west of the Mont.