Contemplate the serene surface of Råcksta Träsk. This small lake resides in Stockholm’s western suburbs. Do not let its urban location fool you. Råcksta Träsk plays a vital role in local ecology.
Despite its location near Sweden’s capital Råcksta Träsk provides critical habitat. Despite high lead and copper levels, it is an important breeding ground for frogs. Råcksta Träsk is also of moderate interest for fishing. Birds find some value here too. Three other small lakes dot the nearby landscape. These are Judarn, Kyrksjön and Lillsjön.
Råcksta Träsk’s catchment area is interesting. It is mainly forest and open land within the Grimsta nature reserve. You will also find minor wetlands. About 20 percent consists of residential buildings. Ten percent is roads. A historical mill sits 300 metres downstream. The mill is managed by Vällingby hembygdsförening. This society is devoted to local culture and history. They have limited ability to regulate the water level. West of Råcksta Träsk lies a grass-covered peak. It is made of excavated material. This came from the construction of Vällingby and Hässelby suburbs. Several busy roads and a metro track pass through the catchment area above ground. The Råcksta Crematorium and its cemetery occupy seven hectares.
The lake and surrounding area offer great recreational value. Pathways were arranged around Råcksta Träsk in the 1970s. Angling is popular here. Occasionally, a skating rink appears on the lake in winter.
Local stormwater pipes contribute most of the affluent. Sometimes, these pipes contain oil of unknown origin. Run-off from roads and residential areas also contributes. This brings nutrients, zinc and copper to Råcksta Träsk. High phosphorus levels occur during late winters and summer. Studies between 1991 and 1997 showed metal content in lake sediments. Moderate copper levels were found. The highest lead levels of any Stockholm lake were noted. Raised levels of organic compounds were also detected. Copper levels in the water table were 50 times the national median.
Phytoplankton in Råcksta Träsk is mostly green algae in August. Minor populations of diatoms and golden algae also exist. Cyanobacteria is absent. Rotifers are the most common zooplankton. Copepods, bosminidae, and ciliates also occur.
Aquatic plants are relatively few in Råcksta Träsk. Rigid hornwort dominates the lake floor. Free-floating plants include Lemna minor and yellow water-lily. White waterlily, broad-leaved pondweed, and amphibious bistort can also be found. Shoreline plants include Alisma and slender tufted-sedge. Cyperus-like sedge and reed sweet-grass grow here. You’ll also find yellow iris and purple loosestrife. Common trees include black alder and grey sallow.
A 1996 survey showed crucian carp dominate the fish population. Perch, roach, tench, and common carp also live in Råcksta Träsk. Trout and rainbow trout were introduced in 1992. Signal crayfish are known to live here.
Before dredging in 1973, bird life was abundant. Since then, populations have reduced. Now there is a stable population of mute swan and mallard. Reed bunting and common moorhen also reside at Råcksta Träsk.
The area is an important breeding location for common frog and common toad. Both species are protected. They are classified as of local and regional interest.
Guided tours around Råcksta Träsk are often arranged. These are by foot or bike. The city and the Society for Nature Conservation host them. The nearest metro station is Råcksta. Råcksta Träsk offers a unique glimpse into urban ecology. It shows how nature persists even in developed areas. Take a moment to appreciate this small but important lake.