The species breeds along the wooded shorelines (Kear 2005) of deep lakes, small rivers and streams (Billerman et al. 2020) with moderate currents, in the tundra, boreal and temperate forest zones, as well as on more saline waters such as sheltered shallow bays, inlets, straits or estuaries with sandy rather than muddy substrates. It shows a preference for narrow channels rather than open expanses of water, with islands or islets and spits, projecting rocks or grassy banks (Snow and Perrins 1998). The majority of the species winters at sea, frequenting both inshore and offshore waters, estuaries, bays and brackish lagoons (Billerman et al. 2020) but showing a preference for clear, shallow waters not affected by heavy wave action (Johnsgard 1978). It will also utilise large freshwater lakes on passage (Madge and Burn 1988). It breeds from April or May (later in northern populations) (Kear 2005). The nest is constructed within 25 m of water in a variety of locations such as natural cavities on the ground, burrows (Kear 2005, Billerman et al. 2020), under boulders (Madge and Burn 1988), amongst tree or scrub roots (Snow and Perrins 1998), in tree cavities, artificial nest boxes (Madge and Burn 1988), amongst reeds or on floating reed mats (Flint et al. 1984). Clutch size is normally eight to ten. Its diet consists predominantly of small, shoaling marine or freshwater fish, as well as small amounts of plant material and aquatic invertebrates. This species is fully migratory (Billerman et al. 2020) although in temperate regions it only undertakes short distance movements to nearby coasts (Scott and Rose 1996)

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 mainly in Finland and Sweden, and also notably in Norway and Russia.
It winters largely in Denmark, and also notably in Norway, the United Kingdom, Greenland, Sweden, Germany, Iceland and the Netherlands.

Conservation Actions Underway
CMS Appendix II. EU Birds Directive Annex II. The breeding density of this species increased on islands in the outer archipelago of south-west Finland as a result of feral American Mink (Neovison vison) removal (Nordstrom et al. 2002).

Conservation Actions Proposed
The erection of nest boxes may encourage the use of local areas by this species. Strict legislation on petroleum drilling and transport should be enforced and measures to reduce bycatch implemented and enforced. Important areas should be protected from drainage and other habitat modifications. Research into the impact this species has on fish stocks and ways to minimise conflict should be established.