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 , 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 "" and flows after only 9 km into the Lake of Neuchâtel at Yverdon-les-Bains. A commercial waterway of this nature would have had a very significant impact on the European commercial transportation system.