You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Rhine

Context:
The Rhine emerges from Lake Constance, flows generally westward, as the Hochrhein, passes the Rhine Falls, and is joined by its major tributary, the river Aare. The Aare more than doubles the Rhine's water discharge, to an average of nearly 1,000 m3/s (35,000 cu ft/s), and provides more than a fifth of the discharge at the Dutch border. The Aare also contains the waters from the 4,274 m (14,022 ft) summit of Finsteraarhorn, the highest point of the Rhine basin. The Rhine roughly forms the German-Swiss border from Lake Constance with the exceptions of the canton of Schaffhausen and parts of the cantons of Zürich and Basel-Stadt, until it turns north at the so-called Rhine knee at Basel, leaving Switzerland.

Question:
What is the major tributary for the Rhine? 

Aare