 Opposite Bremen's "Altstadt" is the point where the "Middle Weser" becomes the "Lower Weser" and, from the area of Bremen's port, the river has been made navigable to ocean-going vessels.The region on the left bank of the Lower Weser, through which the Ochtum flows, is the Weser Marshes, the landscape on its right bank is part of the Elbe-Weser Triangle.The Lesum, and its tributaries, the Wümme and Hamme, the Schönebecker Aue and Blumenthaler Aue, are the downstream tributaries of the Weser.