The common merganser is a large duck, of rivers and lakes of forested areas of Europe, northern and central Asia, and North America. It eats fish and nests in holes in trees.
It is 30 in long with a 38 in wingspan, and a weight of 2.1 kg. Males average slightly larger than females but with some overlap. It has a crest of longer head feathers, but these usually lie smoothly rounded behind the head, not normally forming an erect crest.