Adults can range from 24 to 40 inches in length with a 4 to 5 foot wingspan. The weight can vary from 3.6 to 17.6 pounds. Breeding adults have a black head, white underparts, and a checkered black-and-white mantle. Non-breeding plumage is brownish, with the chin and foreneck white. The bill is black-blue and held horizontally.
This species winters on sea coasts or on large lakes.