The river Thielle (French: La Thielle, or La Thièle, German: Zihl) is a tributary to the Aare , in the Swiss Seeland.

The Thielle results from the merging of the Orbe and Talent, northeast of the little city of Orbe in the Swiss canton of Vaud. It flows as a channel northeastwards through an intensively cultivated plain called "Plaine de l'Orbe" and flows after only 9 km into the Lake of Neuchâtel at Yverdon-les-Bains .

The natural course of the river was considerably modified during the Jura water correction. Between the Lakes of Neuchâtel and Biel/Bienne it was converted into a dug-out channel. However, the previous natural bed of La Thielle still exists in some parts.