The species is restricted to water close to the shore and less than 10 m deep (Scott and Rose 1996). When breeding the species shows a preference for oligotrophic lakes devoid of fish (Kear 2005) but with abundant invertebrate life (Johnsgard 1978), and requires tree-holes (or artificial nestboxes) for nesting. Suitable habitats include freshwater lakes, pools, rivers (Carboneras et al. 2014) and deep marshes (Johnsgard 1978) surrounded by coniferous forest (Carboneras et al. 2014). The species winters mainly at sea (Scott and Rose 1996) on inshore waters, estuaries, coastal lagoons (Carboneras et al. 2014) and shallow bays (Kear 2005), especially in the vicinity of sewage outfalls (Carboneras et al. 2014). Further to the south and on migration the species may also frequent large rivers, lakes and reservoirs (Scott and Rose 1996). The species breeds from April in solitary pairs. The species nests in hollows of mature trees (Carboneras et al. 2014) formed by woodpeckers or by bacterial or fungal heart-rot invasions (Kear 2005). The species will also nest in artificial nest boxes. Clutches are usually between eight and eleven. It feeds predominantly on aquatic invertebrates such as molluscs, worms, crustaceans, aquatic insects and insect larvae, as well as amphibians, small fish and some plant material (mainly in the autumn) such as seeds, roots and the vegetative parts of aquatic plants (Carboneras et al. 2014). Most of this species is fully migratory although it may only travel short distances (Kear 2005), but certain populations in the north-west of Europe may also be sedentary (Carboneras et al. 2014).

Although the generation length for both EU and Europe regional assessments were calculated using the same methodology, new information arriving after the EU assessments were undertaken gave rise to an update in the generation lengths. This new information was then used for the Europe level assessments giving rise to a difference between the generation lengths used for the EU and Europe regions.

In Europe, this species breeds largely in Russia, with notable populations also found in Finland and Sweden.
In winter, this species occurs notably in Sweden, Denmark, Germany, Estonia, Norway, Poland and the United Kingdom.

Conservation Actions Underway
CMS Appendix II. EU Birds Directive Annex II. In some areas nestbox erection programmes have been shown to cause significant range expansions and population increases (Dennis 1987, Carboneras et al. 2014), although an experiment in southern Finland found that even though nestbox provision increased breeding numbers of the species there was a negative density-dependent effect on reproductive output (i.e. the number of fledged young did not increase despite an increase in breeding pairs) (Poysa and Poysa 2002).

Conservation Actions Proposed
In general nesting habitats may benefit from a more extended rotation of timber harvesting (Kear 2005) and the species may benefit from the introduction of strict legislation on oil transportation. Monitoring and research should be introduced to determine the impact of hunting on this species.