Igelbäcken (Swedish: Leech Rill) is a small stream in northern Stockholm, Sweden. The drainage area, part of the national park Ekoparken and divided into several nature reserves, is shared by the municipalities of Järfälla, Sollentuna, Solna, Stockholm, and Sundbyberg.
Stretching more than 10 kilometres west to east from Säbysjön in Järfälla to Edsviken near the Ulriksdal Palace, Igelbäcken's main feeder is the stream Djupanbäcken carrying water from the small lake Djupan. Due to the location in the national park, its untouched character, and to the rare population of Stone Loach, Igelbäcken is considered one of the most valuable water bodies in Stockholm. Nevertheless, samples taken in 2001 showed levels of phosphorus and nitrogen were moderate while levels of metals were increasing between the stream's origin and mouth. The municipalities sharing the catchment area, together with the county administrative board have initiated various project to enhance the natural value of the river and the surrounding green areas. For example, in 2006 Solna and Sundbyberg declared their ambitions to transform the central part of the stream from a straight ditch to a meandering river murmuring over stones, overshadowed by trees and flanked by wetlands intended to attract amphibians and waders; a project partly financed by the Swedish state.
The upper part of the watershed is constituted of Norra Järvafältet, an open-air area characterized by moraine ridges covered with forests separated by water meadows and tilled fields. While some 20 hectares of the surrounding area is used for pasture, the stream is bordered by deciduous plants such as Alder and Birch and Bulrush can be found in non-shadowed patches. Some 2,5 kilometres from its origin, the stream passes down in a culvert under a traffic route (Akallavägen) and the Barkarby Airport before merging with the stream Djupanbäcken. This part of the catchment area contains a motocross track, a golf driving range, a closed dump, and receives stormwater from the E18 traffic route. Thereafter, the stream flows some 4 km in the valley separating the suburbs Akalla-Hjulsta and Tensta-Rinkeby and where are several rural structures including an ecological farm (Hästa Gård), eight allotment-gardens, and some minor overgrown wetlands. East of the valley the river is crossed by a second traffic route (Kymlingelänken) before flowing 2,5 km through an open grassland to reach a railway and the E4 traffic route, water from the latter treated in a local cleaning plant. The last 1.4 km passes more allotment-gardens and the gardens of the Ulriksdal Palace before jumping into Edsviken through a low dam.
In the early 1970s, the stream lost almost a third of its watershed below lake Säbysjön in connection with the construction of a drainage system for the surrounding suburbs. Water leaking into the stormwater tunnel further diminishes the inflow of groundwater. Furthermore, a by-product of the construction of these suburbs were the contaminated tips still located in the catchment area. Though the inflow from Lake Säbysjän remains poorly documented, the lake is known to be rich in nutrients and consequently levels of phosphorus and nitrogen are high in the stream. Below the lake, the drainage area itself brings 120 kg/year of phosphorus and 3.300 kg/year of nitrogen, most of which comes from unsettled and cultivated terrain, a leakage reduced by keeping uncultivated zones next to the watercourse. Contributions of metals, such as zinc and copper, are brought to the stream from the surround open terrain and the landfill deposits in the catchment area. While levels of cadmium, copper, zinc, and nickel were reported as increased in ditches draining these deposits, levels of oil, PCB, and chlorinated hydrocarbons were reported as insignificant.