The Hamme (in its upper reaches Giehler Bach) is a 48 km (30 mi) long river in Germany, Lower Saxony, north-east of Bremen. Its source is north of Osterholz-Scharmbeck. It flows through the moors north-east of Bremen called Teufelsmoor, and meets the river Wümme in Ritterhude. From this junction, the river is called Lesum. The Lesum flows into the river Weser in Bremen-Vegesack.