|Location||Halland County, Västra Götaland County, Sweden|
|Coordinates||57°28′36″N 12°20′22″E / 57.47667°N 12.33944°ECoordinates: 57°28′36″N 12°20′22″E / 57.47667°N 12.33944°E|
|Max. length||20 km|
|Max. width||2.5 km|
|Surface area||33 km²|
|Max. depth||50 m|
|Surface elevation||15 m|
|Settlements||Fjärås kyrkby, Sätila|
Lygnern is a lake in the municipalities of Kungsbacka and Mark, western Sweden. With an area of 33 km², it is the largest lake in Halland County. Its main outflow is Rolfsån, which in turn empties out into the Kungsbacka Fjord.
The lake serves as a source of drinking water for Kungsbacka. In 2006, it was nominated as the cleanest lake in Sweden, as 98% of the surveyed residents of the municipality were satisfied with the water quality.