Mergus merganser, commonly known as the Common Merganser or Goosander, is native to the Northern Hemisphere. Its geographical distribution includes North America, Europe, and Asia. In North America, it is found across Canada, Alaska, and the northern United States. In Europe, it is present in countries such as Norway, Sweden, Finland, and Russia. In Asia, it ranges across Siberia and parts of Mongolia and northern China.

The Common Merganser primarily inhabits freshwater environments such as rivers, lakes, and reservoirs. It prefers clear, cold waters with forested shores. During the breeding season, it nests in mature forests near large bodies of freshwater. In winter, it may move to coastal waters, estuaries, and large rivers that remain ice-free, especially in more temperate regions.

Mergus merganser is a piscivorous bird, meaning its diet consists mainly of fish. Its ecological role includes helping control fish populations in its habitat. This species often preys on small to medium-sized fish, and its serrated bill aids in gripping slippery prey. It is well-adapted to diving and will often submerge to chase fish. The Common Merganser's choice of clear-water habitats allows it to see and catch fish more efficiently.