Large-size duck, thick beak with slightly round culmen. The courting adult beak is black, bluish grey for the adults during winter and for the juveniles, but the culmen is always dark. During winter, their crown and nape are darker than their back; the nape darkness stretches to the sides of the neck, but there is a white band further up; alot of adults’ eyes are surrounded by white, whereas the pale and the dark parts of the face are more blended on juveniles.
It has an upstraight forehead, an angled crown in the front, and it horizontally holds its head. Juveniles scapulars are white striped, that is what differentiates them from the adults which have plainer backs during winter. The juvenile plumage is kept during winter, after which a partial mutation takes place in spring. Visible when they swim, most adults keep their spotted top coverts during winter. In flight, the stockier head and feet help to distinguish it from the arctic loon, pacific loon, and red-throated loon.
The strong yodeling call is heard throughout the year, but most importantly on nesting locations. As many others, it nests on large lakes. It migrates over water like the yellow-billed loon, while the other loons fly lower. It winters mostly in coastal waters or on wide ice-free water stretches.