Located just 60 kilometres north-west of Stockholm, Hjälstaviken is a shallow, almost completely enclosed freshwater embayment of Lake Mälaren, characterized by extremely clear water and overgrown by reedbeds. The bay comprises extensive marshland and the wetland is surrounded by damp meadows and pasture, giving way to drier grassland and arable fields with patches of deciduous and coniferous woodland. About 100 bird species nest in the area, with 40 species linked to wetlands. The Site is important for wintering raptors, including the white-tailed eagle Haliaeetus albicilla. It supports various species of staging waders and Anatidae (ducks, geese and swans). 30% of the Fennoscandia/Eastern Mediterranean population of the globally vulnerable (and critically endangered in Sweden) lesser white-fronted goose is present. Visitor facilities include a trail around the lake and a wheelchair-accessible birdwatching tower. A short boardwalk through the vegetation in the shallow parts of the lake ends with a birdwatching hide. The main threats to the Site are the presence of American mink, an invasive alien species, and pollution from agricultural and forestry effluents.