Drifting islands

Flytholmarna ute i vattnet are noted nesting sites for birds. One of the islands floated away in October 1977, but floated back again. Stockholms Stad has built a dam for water regulation against the marshland west of the lake and from there, Långsjön's water runs further through the Kungens Kurva area and out into Mälaren at Vårby. The dam is also a bridge to the Stockholm side of Långsjön.

Flytholms, also known as floating islands, usually occur in regulated lakes that are near peatlands. It can be peat that sheds from the shores or flooded land that rises. They usually come when the dam is removed in the spring after ice loss. Floating islands are usually 25-30 meters long, but they can become up to a hectare large. It is not uncommon to have multiple floating islands in a lake. Floating islands occur, among others, in lakes Sommen, Lundsjön-Dammsjön, Nimmern and Pirttijärvi. Some lakes in Dalarna have so many floating islands that it is difficult to navigate.

Sources: Huddinge kommun, Svenska Dagbladet https://www.svd.se/a/JoVLMm/mystiskt-flytande-oar-forvanar-men-ar-vanliga