The Aller is a long river in the states of Saxony-Anhalt and Lower Saxony in Germany. It is a right-hand, and hence eastern, tributary of the River Weser and is also its largest tributary. Its last form the Lower Aller federal waterway (Bundeswasserstraße). The Aller was extensively straightened, widened and, in places, dyked, during the 1960s to provide flood control of the river. In a long section near Gifhorn, the river meanders in its natural river bed.