The Aar (German Aare), a tributary of the Rhine, is the longest river that both rises and ends entirely within Switzerland.
Its total length from its source to its junction with the Rhine comprises about 295 km (183 miles), during which distance it descends 1,565 m (5,135 ft), draining an area of 17,779 km2 (6,865 sq mi).
The Aar rises in the great Aar Glaciers of the Bernese Alps, in the canton of Bern and west of the Grimsel Pass. It runs east to the Grimsel Hospice, below the Finsteraarhorn, and then northwest through the Haslital, forming on the way the magnificent Handegg Waterfall, 46 m (151 ft), past Guttannen, and piercing the limestone barrier of the Kirchet by a major canyon, before reaching Meiringen, situated on a plain. A little past Meiringen, near Brienz, the river expands into Lake Brienz where it becomes navigable. Near the west end of the lake it receives its first important tributary, the Lütschine. It then runs across the swampy plain of the Bödeli between Interlaken and Unterseen before flowing into Lake Thun.
Near the west end of Lake Thun, the river receives the waters of the Kander, which has just been joined by the Simme. On flowing out of the lake it passes through Thun, and then flows through the city of Bern, passing beneath eighteen bridges and around the steeply-flanked peninsula on which the Old City is located. The river soon changes its northwesterly flow for a due westerly direction, but after receiving the Saane or Sarine it turns north until it nears Aarberg. There, in one of the major Swiss engineering feats of the 19th century, the Jura water correction, the river, which had previously rendered the countryside north of Bern a swampland through frequent flooding, was diverted by the Hagneck Canal into Lake of Bienne. From the upper end of the lake the river issues through the Nidau-Büren channel and then runs east to Büren. The lake absorbs huge amounts of eroded gravel and snowmelt that the river brings from the Alps, and the former swamps have become fruitful plains: they are known as the "vegetable garden of Switzerland".
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