Havel (häˈfəl) [key], river, c.215 mi (350 km) long, rising in the lake region of Mecklenburg, N Germany. It flows generally S through West Berlin to Potsdam where it turns west. At Brandenburg it turns northwest and enters the Elbe River near Havelberg. It is navigable for most of its length. The Spree River, its chief tributary, joins it at Spandau. The Havel is linked with the Oder River by the Oder-Spree Canal. During the Soviet blockade of Berlin (1948) the Havel was used as a runway for amphibian aircraft.