P. hydrobothynus is a sexually dimorphic species of otter. The male otters have very large and colorful mane made of orange, yellow, and red and a dark brown body with a white underside. They have a short stocky body, a short fat tail, and a much more robust pectoral girdle. Males are usually only 1 meter long, and 0.35 meters tall. The female otters are dark brown in color with a white underside and are camouflaged in the murky water and muddy banks. The female stellar river otters are built like a traditional river otter and are very streamline with a long wing-like tail, and a longer skinnier body. Females tend to be roughly 1.2 meters long, and are 0.2 m tall. The male and female both have very thick fur to stay dry and for insulation. The two sexes are so morphologically different they were first thought to be different species; however, a distinct red diamond pattern on the chest of this species was the first clue that the discoverers had in determining they were the same species.