They have a long, slender beak, above which rises a sharply differentiated, bulging forehead. The eyes are small, and in some species, appear atrophied. Unlike most other cetaceans, platanistids have a distinct neck. The flippers are broad and either rounded or sharply curved. The dorsal fin is low in all but the La Plata dolphin, in which it is moderately high.
Colors tend to be muted grays, pinks, and browns, usually darker above and paler below.
The zygomatic arch is strongly developed and arched. The teeth of most species are simple pegs, but in one species the posterior teeth are slightly tricusped, and in another they have a well defined cingulum. The rivers used by most platanistids are muddy, and these animals probably rely on echolocation more than vision to locate their prey. They feed on fish and invertebrates, making dives that rarely last more than a few minutes. Group size varies from single individuals to 10 or 12.