Unlike other dolphins, Irrawaddy dolphins lack a beak and have flexible necks. The flexibility in the neck causes visible creases behind the head. Additionally, Irrawaddy dolphins have bulging heads, with the forehead extending past the mouth, broad triangular, paddle-like, pectoral fins, and small, triangular dorsal fins set approximately two-thirds of the body length along the back. Skin coloration varies from slate-blue to slate-gray with a lighter underside. The face and head are similar in appearance to beluga whales (Delphinapterus leucas). Irrawaddy dolphins have narrow, pointed, peg-like teeth about 1 cm in length in both the upper and lower jaws. Body mass varies from 114 kg to 143 kg and the length ranges from 146 cm to 275 cm. Males tend to be larger in mass and length, with a larger dorsal fin. Irrawaddy dolphins lack a cardiac sphincter and the stomach is subdivided into compartments.

Range mass: 114 to 133 kg.

Average mass: 124 kg.

Range length: 146 to 275 cm.

Average length: 210 cm.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: male larger