Semnon

Semnon
Country	France
Basin features
Main source	Congrier 90 m (300 ft) 47°47′30″N 01°08′34″W / 47.79167°N 1.14278°W / 47.79167; -1.14278
River mouth	Vilaine 7 m (23 ft) 47°53′59″N 01°45′25″W / 47.89972°N 1.75694°W / 47.89972; -1.75694Coordinates: 47°53′59″N 01°45′25″W / 47.89972°N 1.75694°W / 47.89972; -1.75694
Progression	Vilaine→ Atlantic Ocean
Basin size	400 km2 (150 sq mi)
Physical characteristics
Length	73.3 km (45.5 mi)
Discharge	Average rate: 2.8 m3/s (99 cu ft/s)

The Semnon (French: le Semnon) is a 73.3 km (45.5 mi) long river in the Mayenne, Maine-et-Loire, Ille-et-Vilaine and Loire-Atlantique départements, western France. Its source is at Congrier. It flows generally west-northwest. It is a left tributary of the Vilaine into which it flows between Pléchâtel and Bourg-des-Comptes.

This list is ordered from source to mouth:

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Wikipedia