The Hardhead is a medium-sized duck which appears mainly chocolate brown when swimming, with a white undertail. In flight, the underwings are white, edged with brown. A white belly patch is obvious in flight and when standing in the shallows. The bill is pale blue on the tip. Males have a distinct white eye, while the eye is brown in females. When flying, the wings make a distinctive whirring sound. Hardheads sit low on the water and are diving ducks.