Shallow (average depth 1 m), almost enclosed bay of Lake Mälaren, surrounded by wet, tussocky meadows which merge into drier pasture and fields. Deciduous copses overlook the bay and there is a conifer-covered hill with bare rock outcrops along the eastern edge. Only 30 ha of open water remain, the rest being choked by invasive Phragmites, Scirpus and Typha.
The IBA supports important numbers of passage wildfowl, and the surrounding arable land is an important feeding area. Species of global conservation concern that do not meet IBA criteria: Anser erythropus (up to 5 passage birds), Crex crex (1-3 breeding pairs) and Gallinago media (5-10 passage birds).
Pressure/threats to key biodiversity
Threats include overgrowth of grassland vegetation due to undergrazing and the effects of introduced American mink Mustela vison. Submerged aquatic vegetation has been greatly impoverished in recent years and this, together with the decreasing area of open water, has resulted in the decline of some bird species, notably ducks (`Other' threat). The water-level is artificially manageda more beneficial management regime was decided upon in 1996.
National High International High820 ha of IBA covered by Nature Reserve (Hjalstaviken, 821 ha). 770 ha of IBA covered by Ramsar Site (Hjälstaviken, 770 ha). IBA overlaps with Special Protection Area.
BirdLife International (2021) Important Bird Areas factsheet: Lake Hjälstaviken. Downloaded from
http://www.birdlife.org on 22/01/2021.