The American White Pilican is a large aquatic bird. It breeds in interior North America, moving south and to the coasts, as far as Central America, in winter.
It is a very large and plump bird; its overall length is about 170 cm, courtesy of the huge beak which measures 370 mm in males and 260–330 mm in females. It has a wingspan of about 300 cm and weighs between 9 kg. The plumage is almost entirely bright white, except the black primary and secondary remiges, which are hardly visible except in flight. From early spring until after breeding has finished in mid-late summer, the breast feathers have a yellowish hue. After moulting into the eclipse plumage, the upper head often has a grey hue, as blackish feathers grow between the small wispy white crest.
The bill is long and flat, with a large throat sac, and in the breeding season vivid orange like the iris, the bare skin around the eye, and the feet. In the breeding season, there is a laterally flattened ''horn'' on the upper bill, about one-third the bill's length behind the tip. This is shed off after the birds have mated and laid their eggs, and outside the breeding season the bare parts become duller in color, with the naked facial skin yellow and the bill, pouch and feet an orangy-flesh color.
Apart from the difference in size, males and females look exactly alike. Immature birds have light grey plumage with darker brownish nape and remiges. Their bare parts are dull grey. Hatchlings are naked at first, then grow white down feathers all over, before moulting to the immature plumage.