Spree River, B. Backhaus–Pohl/ZEFA river in northeastern Germany, rising in the Lusatian Mountains just above Neugersdorf and flowing north past Bautzen and Spremberg, where it splits temporarily into two arms. After it passes Cottbus, the river divides into a network of channels, forming a marshy wooded region that is known as the Spree Forest as far as Lübben. It then passes Fürstenwalde and Köpenick and winds through Berlin in several branches to join the Havel River (a tributary of the Elbe) at Spandau after a course of 250 miles (403 km). The Spree drains an area of 3,900 square miles (10,100 square km). A considerable portion of the Spree Forest is now cultivated (market gardening) and also serves as a popular excursion area for Berliners. The Spree River is connected with neighbouring rivers by canals, the most important of which is the Oder-Spree Canal running southeast from Berlin.