Neckar. The Neckar (German pronunciation: [??n??ka??]) is a 362-kilometre-long (225 mi) river in Germany, mainly flowing through the southwestern state of Baden-W??rttemberg, with a short section through Hesse. The Neckar is a major right tributary of the Rhine. Rising in the Schwarzwald-Baar-Kreis near Schwenningen in the Schwenninger Moos conservation area at a height of 706 m (2,316 ft) above sea level, it passes through Rottweil, Rottenburg am Neckar, Kilchberg, T??bingen, Wernau, N??rtingen, Plochingen, Esslingen, Stuttgart, Ludwigsburg, Marbach, Heilbronn and Heidelberg, before discharging on average 145 m3/s (5,100 cu ft/s) of water into the Rhine at Mannheim, at 95 m (312 ft) above sea level, making the Neckar its 4th largest tributary, and the 10th largest river in Germany. Since 1968, the N