Blastocerus dichotomus is the largest South American deer, recognizable in part by its large multitined antlers of eight to ten points when mature. Head-body length is usually just under two meters, with shoulder height from 1.0 to 1.2 metres. The pelage is reddish brown in the summer, turning a darker brown in the winter. The tail is reddish orange, bushy and 10 to 15 cm in length. Marsh deer have large feet with an elastic membrane between the hooves, which may help to keep them from sinking in the mud of their preferred marshy habitat. The legs are black below the carpal/tarsal joints, and there is a black band on the muzzle. Marsh deer have white eye rings and borders of the ears.