The river Ternoise (French pronunciation: [tɛʁnwaz]; Dutch: Ternaas) is one of the small chalk streams that flow from the plateau of the southern Boulonnais and Picardy, via the Canche, into the English Channel. The basin of the Ternoise extends to 342 square kilometres (132 sq mi) and lies in the southern end of the département of Pas-de-Calais. It is one of the rivers of the Seven Valleys tourist area and gives its name to the Ternois area.

The 41.4-kilometre (25.7 mi) long river rises at Ligny-Saint-Flochel and passes through Saint-Pol-sur-Ternoise to join the river Canche at Huby-Saint-Leu, near to the town of Hesdin.

The Ternoise flows through the following places (all within the Pas-de-Calais department):

• Ligny-Saint-Flochel, Roëllecourt, Saint-Michel-sur-Ternoise, Saint-Pol-sur-Ternoise, Gauchin-Verloingt, Hernicourt, Wavrans-sur-Ternoise, Monchy-Cayeux, Anvin, Teneur, Érin, Tilly-Capelle, Blangy-sur-Ternoise, Blingel, Rollancourt, Auchy-lès-Hesdin, Le Parcq, Grigny and Huby-Saint-Leu.

The Faux and the Eps are the only principal watercourses joining the Ternoise.

The Ternoise is a very uniform river. Seasonal flow fluctuations are not very marked, similar to the Canche or the Somme, its neighbours. The higher water flows occur at the end of winter and in the spring. Average flows vary between 3.44 m³ per second in September to 5.36 m³ per second in March.

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  The Ternoise at Hernicourt
• 
  The Ternoise at Auchy-lès-Hesdin
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  The Ternoise at Anvin
• 
  At Anvin, further upstream

• Schéma directeur d'aménagement et de gestion des eaux

• Carte Géologique de la France à l'échelle du millionième 6th edn. BRGM (2003) ISBN 2-7159-2158-6
• Banque Hydro - Station E5406510 - La Ternoise à Hesdin (option Synthèse)
• Carte des bassins versants de la Canche et de la Ternoise
• Informations sur les atlas des zones inondables