The head-and-body length is typically between 177–235 cm (70–93 in) and the average height is between 120 and 136 cm (47 and 54 in). A sexually dimorphic antelope, males are taller as well as heavier than females. Males reach approximately 127 cm (50 in) at the shoulder, while females reach 119 cm (47 in). Males typically weigh 198–262 kg (437–578 lb) and females 161–214 kg (355–472 lb). The coat colour varies from brown to grey. The long, ridged horns, present only on males, curve backward, then forward and are 55–99 cm (22–39 in) long.

Waterbucks have a brownish-grey shaggy coat. The eyes and nose are patched with white, and there is a white collar under the throat. The rump has a characteristic white ring. The large rounded ears are a prominent feature. Only the bulls have long, forward curved horns. Both sexes emit a, not unpleasant, musky smell which normally lingers at resting sites.