Pacific Loon has a smoothly rounded head and neck and a straight bill. In breeding plumage, the top of the head and back of the neck are pale gray, lighter than the face. The body is black with white markings. Non-breeding plumage is dull black-brown, duller black on the back, and dark brown on the sides. Chins, throats, and breasts are all white, with a dark necklace at the top of the throat. The back of the head is gray, much darker than in breeding plumage.