|Location||Lower Saxony, Germany|
|Length||14.2 km, including the Hahnenbach 35.2 km|
|Source||confluence of the Hahnenbach and Mehlandsbach near Bellen
|Source height||33 m|
|Mouth||near Rotenburg into the Wümme
|Mouth height||18 m|
|Progression||Wümme → Lesum → Weser → North Sea|
|Discharge||Average mid: ca. 3.0 m³/s; before it joins the Rodau: 1.6 m³/s|
The Wiedau is a left-hand tributary of the Wümme in the north German state of Lower Saxony. The river begins near Bellen in the vicinity of Hemslingen in the district of Rotenburg (Wümme) at the confluence of the Hahnenbach and the Mehlandsbach, flows through the collective municipality of Bothel, a densely wooded and near natural depression, and discharges into the Wümme in Rotenburg shortly after being joined by the only slightly smaller Rodau.
The Wiedau is popular with anglers and canoeists. At high water, the Wiedau can be navigated from the road bridge in Bellen near Hemslingen to its mouth on the Wümme by small kayaks, a distance of 23 km.