[1] The lake is shared between the administrative kommunes of Ydre, Kinda, Boxholm and Tranås and the area around it is sparsely populated.

[2] In and around the lake various rare species are protected in a series of nature reserves,[5] bird sanctuaries[1] and areas closed for fishing.

[1] The visitor centre and natural history museum, Naturum Sommen, lies at the northern end of Torpön island, near the central part of the lake.

According to the Svensk ortnamnslexikon the lake name was given as Sooma in 1447 and is derived from the local dialect word somma meaning an oversized vessel.

[6] Scholar Robert Norrby considered that the name Sommen originated as a noa-name - an unknown sacred or taboo name that the lake had.

[8] In 1568, amidst the Northern Seven Years' War, a Danish raiding party led by Daniel Rantzau managed to escape back to Denmark by crossing over the frozen lake, avoiding Swedish defences to the west and east.

Sommaskep are for rowing, and differ from ordinary small traditional wooden boats in Sweden for having a longer stem.

An explanation for this design is that it makes boats easier to navigate in the typically short-wavelength waves of Sommen.

The plants are Vicia pisiformis and the orchids Ophrys myoides, Malaxis monophyllos and Herminium monorchis.

[20][D] Geographically the lake lies within the South Swedish highlands at a place where the Sub-Cambrian peneplain is uplifted.

[17][25][26] Topography displays local height differences as large as 100 m.[26] Granite weathered into grus can be found at various locations around the lake.

[20] Following its maximum extent about 20,000–17,000 years ago the Fennoscandian ice sheet began to shrink gradually.

[29] These are near the lake's eastern shores with patterned ground which presumably formed during the periglaciation of the area during the Younger Dryas.

[30] The biogeography of various aquatic species deemed glacial relicts that are found in Sommen is likely related to a different geography during the early history of the lake.

One theory claims that aquatic species were transferred from the Baltic Ice Lake through a natural lock system in connection with a temporary advance of the ice-front during the Younger Dryas.

[29] On land, the unusual occurrence of dwarf birch near Sund is also judged to be a leftover from a cold geological past.

This means the lake is being slowly tilted and the southeastern shores drowned while near the outlet land is being dried up.

[31] Large birds that breed in the area include fish hawk, European herring gull, heron and black-throated loon.

[37] Lek locations lie chiefly along the eastern shores of Norravifjärden and around Malexander in the north-central parts of the lake.

The lake stands out for having three crustacean species that are relicts from the time of the Fennoscandian Ice Sheet deglaciation about 12,000 years ago.

Neither is there any considerable acidification as seen in other Swedish lakes; however high cadmium and fluoride contents are an environmental concern.

[1] Extremely high concentrations of dioxin have been found in the vicinity of Brandnäs sågverk, a former lumber mill that closed in the 1950s.