The Birs has its source in a spring near the
Col de Pierre Pertuis at above sea level a little southwest of
Tavannes in the
Jura bernois. It starts as a proper river; the large amount of water is the product of an extended underground river system. The Birs runs through wider valleys (Vallée de Tavannes) and narrow gorges. Near
Delémont, the capital of the canton of Jura, it joins the
Sorne and the
Scheulte. Between
Soyhières and
Liesberg, it leaves the French-speaking part of Switzerland, enters the canton of
Basel-Landschaft and receives the
Lützel from the left. In
Laufen it forms a waterfall, which was the source of power and of the name of the city. At the gorge of
Angenstein, the river runs into the
Birseck, the lowland by
Aesch. Between Aesch and
Dornach, the Birs is rich in fresh-water crabs, the native species of which are now threatened by the American red crab. Earlier, the Birs was polluted and dammed, but it has largely been restored to its original state. The
Reinacherheide is a wildlife preserve with 83 species of bird. The mouth of the Birs was hardly settled until the 18th century. Today, the city of
Birsfelden stands there. The lower stretches of the Birs form the border between
Basel-Stadt and Basel-Landschaft. In 2004, it was restored from a concrete canal to a more natural river. Beavers have even been sighted along the river. The Birs also forms the border between the cities of
Basel and
Birsfelden. It flows into the Rhine at
Birskopf after . ==See also==