Vänern (vĕ´nərn), lake, c.2,145 sq mi (5,560 sq km), SW Sweden, fed by the Klarälven and drained by the Götaälv SW into the Kattegat. It is the largest lake in Sweden and the third largest in Europe. The deep lake, traversed by the Göta Canal, accommodates small oceangoing vessels. There are vast stands of forest north of the lake; pulp and paper mills line the shore. Karlstad is the principal city on the lake.