River Aver

The River Aver may be traced to the mountain stream of the Black Mountains and is most notable for its strong blue colour and vigorous, foaming waters. Its upper reaches contain many waterfalls, but by the time it joins the Reik, the river is large and easily navigable by river boat and barge. It also passes through the heart of the Moot - the Halfling territory - where it is a vital irrigation source for their agriculture. From time to time it also bears messengers between the great city of Nuln and the distant Dwarfen fortress of Karak-Varn, high in the Black Mountains.

Source
Warhammer Fantasy RPG 1st Edition -- pg. 283