Adults can range from 61–100 cm (24–40 inches) in length with a 122–152 cm (4–5-foot) wingspan. The weight can vary from 1.6 to 8 kg (3.6 to 17.6 lbs). On average a Great Northern Diver is about 81 cm (32 inches) long, has a wingspan of 136 cm (54 inches), and weighs about 4.1 kg (9 lbs).
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. The Great Northern Diver breeds in Canada, parts of the northern United States, Greenland, and Alaska. On isolated occasions they have bred in the far north of Scotland. The female lays 1 to 3 eggs on a hollowed-out mound of dirt and vegetation very close to water. Both parents build the nest, sit on the egg or eggs, and feed the young. This species winters on sea coasts or on large lakes over a much wider range in Europe and the British Isles as well as in North America.
Chicks will ride their parents' backs This species, like all divers, is a specialist fish-eater, catching its prey underwater, diving as deep as 200 feet (60 m). Freshwater diets consist of pike, perch, sunfish, trout, and bass; salt-water diets consist of rock fish, flounder, sea trout, and herring.The bird needs a long distance to gain momentum for take-off, and is ungainly on landing. Its clumsiness on land is due to the legs being positioned at the rear of the body: this is ideal for diving but not well-suited for walking. When the birds land on water, they skim along on their bellies to slow down, rather than on their feet, as these are set too far back. The loon swims gracefully on the surface, dives as well as any flying bird, and flies competently for hundreds of kilometers in migration. It flies with its neck outstretched, usually calling a particular tremolo that can be used to identify a flying diver.
Its call has been alternately called "haunting," "beautiful," "thrilling," "mystical" and "enchanting."
Great Northern Diver nests are usually placed on islands, where ground-based predators cannot normally access them. However, eggs and nestlings have been taken by gulls, corvids, raccoons, skunks, minks, foxes, snapping turtles and large fish. Adults are not regularly preyed upon, but have been taken by sea otters (when wintering) and bald eagles. Ospreys have been observed harassing divers, more likely out of kleptoparasitism than predation. When approached by a predator of either its nest or itself, divers sometimes attack the predator by rushing at it and attempting to impale it through the abdomen or the back of the head or neck.