Lygnern (Swedish pronunciation: [ˈlʏ̂ŋːnɛɳ])[3] is a lake in the municipalities of Kungsbacka and Mark, western Sweden.

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.

[4] Ten fish species have been found in the lake, which is particularly rich in pike, trout and European perch.