Wümme is a river in northern Germany, in the states Lower Saxony and Bremen, marking the border between the two states for part of its course. It is the main headstream of the Lesum. The Wümme's length is 121 kilometres (75 mi). Including the 9.9 km (6.2 mi) Lesum, that runs into the river Weser, its total length is 131.2 km (81.5 mi). The river's source is on the Wulfsberg in Lüneburg Heath. West of Rotenburg, it takes up the rivers Rodau and Wiedau. The Wümme from the left and the Hamme from the right combine near Wasserhorst (part of Blockland in Bremen) forming the Lesum.