The animal commonly referred to as the Water Rat is Australia’s native semi-aquatic rodent, officially known as the Rakali (Hydromys chrysogaster). This species is often mistaken for introduced pest rats, but it possesses a distinct appearance shaped by its watery habitat, making it easy to distinguish from invasive counterparts.
General Appearance and Size
The Rakali is a relatively large rodent with a robust and streamlined body shape, adapted for moving efficiently through water. Its body length typically ranges between 23 and 37 centimeters, excluding the tail, and it can weigh between 340 grams and 1.275 kilograms, making it one of the largest native rodents in Australia. The overall appearance is one of sturdiness, resembling a small otter more than a common rat.
The fur of the Rakali is extremely dense and thick, with a glossy, water-repellent quality that aids in insulation and buoyancy. Coloration of the coat is typically dark, ranging from black to dark brown or slate-gray across the back and upper body. This dark upper layer contrasts sharply with the underside, which is usually a bright white, cream, or a distinctive golden-orange color.
Specialized Features for Aquatic Life
The Rakali possesses several specialized adaptations for swimming. Its hind feet are noticeably wide and partially webbed, a feature that provides increased propulsion and steering ability in the water. The head is somewhat flattened with a broad face, which contributes to its streamlined profile and helps with underwater movement. The ears and eyes are relatively small, reducing drag while swimming.
The Rakali has a double coat of fur, consisting of a fine underlayer that traps air for insulation and a dense outer layer that repels water. This dense coat ensures the animal stays warm and dries quickly upon leaving the water.
The tail is a particularly distinct feature, acting as a rudder for steering and a counterweight for balance in the water. It is thick at the base and tapers toward the end, possessing a dark color consistent with the rest of the upper body. The most recognizable identifier is the prominent white or pale tip on the tail, which is present in most individuals and serves as a reliable visual marker.
How to Tell a Water Rat from Other Rodents
The Rakali is easily distinguished from introduced pest species, such as the Brown Rat (Rattus norvegicus), by several key visual differences. The Rakali has a broad, blunt muzzle and a flattened head, giving it a face that is less pointed than the common Brown Rat. Its ears are also significantly smaller and less conspicuous, sitting flatter against the head.
A major distinguishing feature is the tail: the Rakali’s tail is thick, well-furred, and often displays the characteristic white tip. In contrast, the tails of introduced rats are typically thin, scaly, and uniform in color, lacking any white tipping. Furthermore, the Brown Rat has unwebbed feet, while the Rakali’s partially webbed hind feet are an immediate indicator of its native, aquatic identity.