Common Water Rat

Identification

The rakali (Hydromys chrysogaster), also known as the water-rat or Australian otter, is a distinctly aquatic rodent measuring 23–37 cm in body length with a thick tail of 24–35 cm. They weigh between 340–1,275 g, with males generally larger than females. The most recognisable feature is their dark tail with a distinctive white tip. Their waterproof coat varies from black to brown on the back, contrasting sharply with an orange to white belly. Look for their flattened head, partially webbed hind legs, long whiskers and small eyes and ears—all adaptations to their semiaquatic lifestyle.

Rakali possess a large, flat and elongated skull, and their streamlined body shape makes them highly specialised for aquatic hunting. Their thick, water-repellent fur provides both protection and insulation in their waterside habitats. Females are noticeably smaller than males, though their tails are typically similar in length.

Range & Habitat

This widespread species is found throughout most of eastern Australia including Tasmania, along the northern coast (except the Pilbara region), and in south-west Western Australia. They also occur in New Guinea and offshore islands. Rakali are highly adaptable, inhabiting any permanent water system from freshwater streams and slow-moving rivers to brackish lakes, estuaries, coastal bays and farm dams. They favour low banks with densely vegetated edges that provide protection while hunting.

Their home range typically spans 1–4 km of waterways, and they can travel 200 metres to 1 km during a single night of foraging. They spend non-foraging hours resting in hollow logs and burrows on waterside banks, emerging as mostly nocturnal hunters.

Behaviour & Diet

Rakali are predominantly carnivorous, feeding on a diverse diet of aquatic prey including fish, crustaceans, molluscs, insects, frogs and small water birds. They also consume eggs, small mammals such as mice, and even bats. These solitary animals hunt at dusk and dawn, using sight while in water and relying on memory of previous catch locations when hunting at the water's edge. In winter, when aquatic prey becomes scarce, they supplement their diet with plants and spend longer periods sheltering in their warm burrows, preferring terrestrial prey during colder months. A notable recent addition to their diet is the heart and liver of toxic cane toads in regions where these invasive amphibians occur.

Rakali are highly territorial and can become aggressive in high-density populations. Fighting is common, particularly among solitary males and females, often resulting in scarred and bitten tails and other wounds.

Best Time & Places to See It

Since rakali are predominantly nocturnal and crepuscular, your best chances of observing them are at dusk and dawn or during night-time observations. Search along the banks of rivers, lakes, estuaries and coastal wetlands throughout eastern Australia, Tasmania, northern Australia and south-west Western Australia. Look for them in areas with densely vegetated, low banks and permanent water. Farm dams, creeks and slow-moving waterways are particularly good locations. Winter offers fewer opportunities as they spend longer periods in their burrows.

Photography Tips

Photographing rakali presents a genuine challenge due to their nocturnal habits and solitary, wary nature. Plan for dawn or dusk shoots near known waterway habitats with vegetated banks. Use a tripod and remote trigger to avoid disturbance, and be prepared with high ISO settings or artificial lighting for low-light conditions. Their distinctive white-tipped tail and orange belly provide striking contrast—try to capture these features against darker water or vegetation. Patience is essential; position yourself quietly near burrows or along favourite feeding routes and wait for them to emerge. Their partially webbed feet and streamlined profile are worth capturing if you can get close enough.