A medium-sized duck, noticeably smaller than a Mallard, with a very large, spoon-shaped bill that is obvious even at a distance and in flight. The breeding male shows a dark green head, white breast, and rich chestnut flanks and belly. The female is buffy-brown but shares the same oversized bill. Both sexes display a pale, chalky-blue patch on the upperwing. It feeds by filtering food from the water, often seen swimming in tight circles in small groups.