Långsjön, Älvsjö 3.05

Långsjön is a lake in southern Stockholm, Sweden. The lake is situated in an old residential neighbourhood located between the municipalities of Stockholm and Huddinge and most of the shoreline is private property. Water level is controlled by a sluice in the north-western end of the lake where the lake empties into Lake Mälaren through a system of dikes and culverts. Polluted waste water was poured directly into the lake during the early 20th century which caused up to two third of the lake to be choked-up until the 1940s. It was subsequently one of the first lakes in Stockholm to be subject for various attempts to restorations. The northern shores are waterlogged whilst the bedrock surfaces along the southern. The lake has no major feeders, the inflow instead coming from local stormwater and surface runoff.Catchment areaSome 60 per cent of the lake catchment area is occupied by settlements, mostly one-family houses but several minor green spaces are scattered around the lake. South-wester of the lake is a small area forming part of the Gömmaren nature reserve. The lake has two bathes.Environmental influenceThe number of polluting operations in the catchment area is limited to a petrol station and an engineering workshop. In the end of the 1930s sewers were built in the area and the waste water fed into the lake during the 1920s and 1930s is today brought to the wastewater treatment works at Henriksdal, but old sewers still leak into the lake and the water was considered unfit for bathing at several occasions during the 1990s. Långsjön is one of few lakes in Stockholm where spillway overflow adds appreciable amounts of phosphorus. Surface runoff adds some 70 kg of phosphorus and 1,000 kg of nitrogen annually and more than half of phosphorus added through surface water is produced by the surrounding one-family houses and their gardens.