a river in the southern Federal Republic of Germany, a right tributary of the Rhine. Length, 371 km; basin area, approximately 14,000 sq km.
The Neckar rises on the slopes of the Black Forest and the Swabian-Franconian Jura, flowing primarily in a narrow, in places canyon-like, valley; it meanders sharply. Average rate of flow at the mouth is 130 cu m per sec, with maximum flow in February and March. It freezes in severe winters. The river is navigable to the city of Plochingen (203 km); there are canals and locks along much of it. The big cities of Stuttgart, Heidelberg, and Mannheim are on the Neckar.