a lake in southern Sweden. Area, 5,500 sq km (the third largest in Europe after Lakes Ladoga and Onega). Length, approximately 140 km; maximum width, 80 km. Maximum depth, 100 m ; elevation, 44 m above sea level. Area of the water basin, approximately 48,000 sq km.
Vänern occupies a tectonic depression—a graben deepened by Pleistocene glaciers and bordered in some areas by fractures and faults. Its shoreline is mainly low and much indented. The lake has many islands. The variations in the level are not considerable and are gradual because of the diversification of the floodwaters of the tributaries flowing into the lake from the north and south and also as a result of the regulation of the flow by a dam. The lake freezes up in December or January and thaws at the end of April. However the ice cover is not firm. More than 30 rivers flow into the lake, the largest being Klarälven. The Göta älv flows out of the lake into the Kattegat. Vänern is part of the inland waterway joining Stockholm and Göteborg, known usually as the Göta Canal. There is navigation throughout the lake; the main ports are Karlstad in the north, Mariestad in the east, and Vänersborg in the southwest.