Mjörn is a lake in Västergötland, shared between the municipalities of Alingsås and Lerum and is part of the main catchment area of the Göta River.

It then continues in the lake Sävelången, Säveån through Lerum and Partille municipalities and into the Göta River in Gothenburg.

The others are northern pike, perch, zander, eel, bream, roach, ide, tench, burbot, ninespine stickleblack, ruffe, vendace and smelt.

There are purely maritime species here that do not normally belong in an inland environment, such as great black-backed gull, eurasian oystercatcher and common eider.

Examples of breeding seabirds are the black-throated loon, osprey, little ringed plover, red-breasted merganser and great black-backed gull.

In 1987, the non-profit association "Mjörns Sjökortsförening" was formed with the aim of creating reliable nautical charts of Mjörn and to manage the marking of a fairway across the lake.

The Säveån river that drains the catchment area has tributary order 2, which means that the water flows through a total of 2 watercourses before reaching the sea after 46 kilometers.

The attractiveness of the environment around the lake is shown by the increased demand for plots and large house constructions in Alingsås.

The villages of Björboholm, Västra Bodarne and Skår, Lövekulle with its large holiday villas, owned by wealthy merchants mostly from Gothenburg, developed alongside both the Western Main Line, whose first sod was turned in Lövekulle outside Alingsås, and the West Gothenburg Line.

According to the county administrative board, Mjörn has also been classified as a lake with "particularly high nature value", meaning the highest possible classification.

The powerful flow of meltwater through the narrow passage in Brobacka carried large stones, shaping the enormous kettles.