The American black duck weighs 720–1,640 g (1.59–3.62 lb) and measures 54–59 cm (21–23 in) in length with a 88–95 cm (35–37 in) wingspan.
This species has the highest mean body mass in the genus Anas, with a sample of 376 males averaging 1.4 kg (3.1 lb) and 176 females averaging 1.1 kg (2.4 lb).
The American black duck somewhat resembles the female mallard in coloration, although the black duck's plumage is darker.
Males and females are generally similar in appearance, but the male's bill is yellow while the female's is dull green with dark marks on the upper mandible, which is occasionally flecked with black.
The head is brown, but is slightly lighter in tone than the darker brown body.
The cheeks and throat are streaked brown, with a dark streak going through the crown and dark eye.
The speculum feathers are iridescent violet-blue with predominantly black margins.
The fleshy orange feet of the duck have dark webbing.

Both male and female American black ducks produce similar calls to their close relative, the mallard, with the female producing a loud sequence of quacks which falls in pitch.

In flight, the white lining of the underwings can be seen in contrast to the blackish underbody and upperside.
The purple speculum lacks white bands at the front and rear, and rarely has a white trailing edge.
A dark crescent is visible on the median underwing primary coverts.

Juveniles resemble adult females, but have broken narrow pale edges of underpart feathers, which give a slightly streaked rather than scalloped appearance, and the overall appearance is browner rather than uniformly blackish.
Juvenile males have brownish-orange feet while juvenile females have brownish feet and a dusky greyish-green bill.
The American black duck weighs 720–1,640 g (1.59–3.62 lb) and measures 54–59 cm (21–23 in) in length with a 88–95 cm (35–37 in) wingspan. This species has the highest mean body mass in the genus Anas, with a sample of 376 males averaging 1.4 kg (3.1 lb) and 176 females averaging 1.1 kg (2.4 lb). The American black duck somewhat resembles the female mallard in coloration, although the black duck's plumage is darker. Males and females are generally similar in appearance, but the male's bill is yellow while the female's is dull green with dark marks on the upper mandible, which is occasionally flecked with black. The head is brown, but is slightly lighter in tone than the darker brown body. The cheeks and throat are streaked brown, with a dark streak going through the crown and dark eye. The speculum feathers are iridescent violet-blue with predominantly black margins. The fleshy orange feet of the duck have dark webbing.
Both male and female American black ducks produce similar calls to their close relative, the mallard, with the female producing a loud sequence of quacks which falls in pitch.
In flight, the white lining of the underwings can be seen in contrast to the blackish underbody and upperside. The purple speculum lacks white bands at the front and rear, and rarely has a white trailing edge. A dark crescent is visible on the median underwing primary coverts.
Juveniles resemble adult females, but have broken narrow pale edges of underpart feathers, which give a slightly streaked rather than scalloped appearance, and the overall appearance is browner rather than uniformly blackish. Juvenile males have brownish-orange feet while juvenile females have brownish feet and a dusky greyish-green bill.
American black duck