The Thérain () is a river in France, tributary of the Oise. It is long. It rises between Saint-Michel-d'Halescourt and Grumesnil in Seine-Maritime at 175 meters elevation. It flows generally southeast, through Songeons, Milly-sur-Thérain, Beauvais, Hermes and Mouy, and joins the Oise at Creil.
Its valley, near the metropolitan area of Paris, has been a highly industrialized and populated area, and Beauvais lies at the foot of wooded hills on the left bank of the Thérain at its confluence with L' Avelon.
Affluents Ruisseau d'Hardouins Le Tahier Ruisseau de Wambez Le Petit Thérain L' Avelon Rivière de Saint-Quentin Rivière de Saint-Just La Liovette Le Wage Ru de Berneuil Fosse d'Orgueil La Laversines La Trye Le Sillet Ru de la Maladrerie Ru de Lombardie Le Moineau Fossé l' Evêque Le Ruisseau de Saint-Claude Le Ruisseau de Cires Le Ruisseau de Flandre
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