The Indian spot-billed duck (Anas poecilorhyncha ) is a large dabbling duck that is a non-migratory breeding duck throughout freshwater wetlands in the Indian subcontinent. The name is derived from the red spot at the base of the bill that is found in the mainland Indian population. When in water it can be recognized from a long distance by the white tertials that form a stripe on the side, and in flight it is distinguished by the green speculum with a broad white band at the base. This species and the eastern spot-billed duck (A. zonorhyncha ) were formerly considered conspecific, together called the spot-billed duck (A. poecilorhyncha ).
This duck is around the same size as a mallard and has a scaly patterned body with a green speculum bordered by white. At rest the white stripe stands out and the long neck and the bill with yellow tip and orange red spots at the base are distinctive in the nominate subspecies. The red spots at the base of the bills are absent in haringtoni. It measures 55–63 cm (22–25 in) in length and 83–95 cm (33–37 in) across the wings, with a body mass of 790–1,500 g (1.74–3.31 lb). These are mainly grey ducks with a paler head and neck and a black bill tipped bright yellow. The wings are whitish with black flight feathers below, and from above show a white-bordered green The male has a red spot on the base of the bill, which is absent or inconspicuous in the smaller but otherwise similar female. The male does not have an eclipse plumage. The legs and feet are bright orange to coral red. Juveniles are browner and duller than adults.
The eastern spot-billed duck is darker and browner; its body plumage is more similar to the Pacific black duck. It lacks the red bill spot, and has a blue speculum.
Both males and females undergo a complete post-breeding moult, dropping all their wing feathers simultaneously.