There are five bad passes, due to the accumulation of trees and rafts of timber.
Its rapid current does not permit of extensive navigation, but timber rafts are floated down from above Innsbruck.
On the eastern side of the river, on the other hand, there are several important tributaries descending from the Persian mountains: the Khabur, a little north of 37° N., navigable for rafts; the Great Zab, at 36° N., just below Nimrud, the ancient Calah; the Little Zab, about 35° 15' N.; the 'Adhem at 34° N.
Taking a northerly course, it quits the mountains at Immenstadt, and, flowing by Kempten, from which point it is navigable for rafts, forms for some distance the boundary between Bavaria and Wurttemberg, and eventually strikes the Danube (right bank) just above Ulm.
Steamers ascend this river as far as Bilyutai, near the Mongolian frontier, and bring back tea, imported via Kiakhta, while grain, cedar nuts, salt, soda, wool and timber are shipped on rafts down the Khilok, Chikoi and Uda (tributaries of the Selenga), and manufactured goods are taken up the river for export to China.