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.