The thick, soft fur is usually dark brown above and golden-orange below. The water rat is common in rivers, streams and estuaries throughout the state. Although primarily nocturnal, it may be seen during the day. Unlike most rodents, the water rat is a predator. Its diet includes aquatic insects, fish and crustaceans.
Breeding can occur throughout the year, with peaks in spring and summer.
Gestation is 35 days. As many as five litters, averaging 3-4 young, can be born each year. The tail is longer than head and body. The species occurs in rainforest and wet and dry sclerophyll forest. Its broad diet includes lichen, bryophytes, ferns, seeds, fruit and some insects.