| Ternoise | |
| Pushpin Map: | France#France Hauts-de-France |
| Mouth Location: | Canche |
| Mouth Coordinates: | 50.3814°N 2.0114°W |
| Subdivision Type1: | Country |
| Subdivision Name1: | France |
| Length: | 41.4km (25.7miles) |
| Discharge1 Avg: | 4.45m3/s |
| Basin Size: | 342km2 |
The river Ternoise (in French pronounced as /tɛʁnwaz/; Dutch; Flemish: 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 342km2 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 41.4km (25.7miles) 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):
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.