After the attainment of sexual maturity, the body colour changes to all white except for the edges of the flippers and flukes, which retain dark pigment. Well-fed belugas have a lumpy appearance, with folds of fat along the sides of the body. The flippers are broad and, in adult males, curl up at the tip. The flukes of adults have a convex rear margin. There is no dorsal fin, but a low, serrated ridge is present along the midline where a fin occurs on other species.
White whales can radically change the shape of their bulbous melon.
The short, broad beak is cleft slightly in the centre. There are 40-44 simple conical teeth evenly distributed in the jaws. Sharp initially, these teeth eventually become badly worn, and many are lost by injury or infection. Experiments have shown them to be adept at echolocation, and judging by the variety of sounds they make, they are also highly communicative. Their sociable nature is manifest in the large size of herds, including up to several thousand individuals, that congregate in river mouths during summer.