The AAR is a river that flows through the Swiss capital of Bern. It is also known as the AARE River, which is the German name for the river. The AAR is the longest river entirely in Switzerland and is approximately 290 kilometers long. It is an important source of hydroelectric power and is used for irrigation and drinking water. The AARE River is a major tributary of the Rhine River and is a popular destination for fishing, swimming, and boating.