Germany, the Jizera in Bohemia and the Isère in France) before assimilation by the Franks.

Tributaries

The main tributaries of the Yser are:
* Peene Becque (Penebeek)
* Sale Becque (Vuilebeek)
* Ey Becque (Heidebeek)
* Zwyne Becque (Zwijnebeek)
*