There are remains of human habitation in the region since the Stone Age, including petroglyphs that are among the oldest in Sweden.

[4] The Enan and Handölan converge just before entering the west of the lake, where the Handöl delta has formed.

[4] Tributaries draining the mountain area to the south and east of the lake include the Västerån, Bunnerån, Järpån, Rekån and Kärrån.

[6] Ånnsjön is part of the sub-basin called the "outlet of Ånnsjön", which has an average altitude of 561 metres (1,841 ft) above sea level and an area of 144.5 square kilometres (55.8 sq mi) When all the upstream drainage basins upstream are counted, the accumulated basin area is 1,562.07 square kilometres (603.12 sq mi).

[8] The shallow Ånnsjön lake and surrounding marsh complex would have provided good resources of fish, waterfowl and other wildlife for the ancient population.

About 60 fishing settlements have been located on the shores of the lake and on the islands of Granön, Årsön and Bunnernäset.

[10] There are records of disputes over the boundaries of the concessions and over fishing rights, and indications that at times the lake was over-fished.

[12] Soapstone artifacts have been manufactured around Handöl village and the west of the lake since at least 1600, and this is still an important industry.

To the west of Handöl there are open pits in the mountain side that testify to mining operations.

[7] In 1897 the English Admiral Sir William Robert Kennedy and his brothers came to Ånnsjön, drawn by the fishing and hunting.

[4] In the second half of the 19th century the villagers dug drainage ditches in the bogs in the hope of converting them into agricultural or forestry land.

As of 2013 the county was starting work to reverse the process by cutting down the birch trees and using them to fill the ditches.

[15] In winter the ice forms quickly on Ånnsjön, and the exposed position keeps snow from accumulating for some time.

Even when the ice is thin, the depth along the beaches is only knee-high, so the lake is favored for training by competitive speed and distance skaters.

[17] The lake is home to the near-threatened great snipe (Gallinago media) and vulnerable long-tailed duck (Clangula hyemalis).

Other resident or breeding birds include the black grouse, western capercaillie, greater scaup, red-throated loon, Arctic loon, common kestrel, merlin, northern harrier, rough-legged hawk, common crane, Eurasian golden plover, Eurasian dotterel, whimbrel, spotted redshank, common redshank, wood sandpiper, Temminck's stint, purple sandpiper, broad-billed sandpiper, ruff, red-necked phalarope and long-tailed jaeger.