Aare (är´ə) or Aar (är), longest river entirely in Switzerland, 183 mi (295 km) long, rising in the Bernese Alps and fed by several glaciers. The upper Aare emerges from dam-impounded Grimsel Lake and flows generally W through Lake Brienz, past Interlaken (where it is canalized), and through Lake Thun, the head of navigation. The Aare continues northwest, flowing through Bern before turning and flowing generally northeast, past Solothurn and Aarau, to join the Rhine River opposite Waldshut, Germany. With its chief tributaries, the Reuss and Limmat rivers, the Aare drains most of Switzerland. The Aare is connected with Lake Biel by two canals. Near Meiringen, the Aare flows through a scenic gorge. There are more than 40 hydroelectric power plants on the river.

Aarau (ä´rou), town (1993 pop. 15,900), capital of Aargau canton, N Switzerland, at the foot of the Jura Mts. and on the Aare River. Manufactures include bells, mathematical instruments, electrical goods, shoes, and other products. Aarau was founded c.1250; it was the temporary capital (1798) of the Helvetic Republic.