Neckar (nĕkˈär) [key], river, 228 mi (367 km) long, rising in the Black Forest, SW Germany. It flows generally N past Tübingen, Stuttgart, and Heilbronn, then W past Heidelberg before joining the Rhine River at Mannheim. The Neckar is celebrated for its scenic charm; its hilly banks are covered with fine vineyards, orchards, and woods. It is navigable for 1,000-ton barges and is connected to the Danube by a canal. There are more than 20 hydroelectric power plants on the river.