Platypus live in relatively pristine waters, which makes them difficult to locate, given the growing number of polluted waterways in our country. But if you keep your eyes open you can get lucky.
They are most likely to be observed early in the morning or late in the evening, but may also be active in the middle of the day. They live in a similar habitat to the Australian water-rat, so be careful you don’t get confused if you spot movement in the water.
Both animals occupy natural lakes, rivers, creeks, backwaters and billabongs, as well as weir pools, irrigation channels and man-made dams or reservoirs. They are generally spotted in places where the water surface is fairly calm, making it easier for observers to identify the ripples formed on the water surface as the animals swim and dive.
Both species occur over a wide altitudinal range, from sea level up to at least 1500 metres. Platypus, however, are not commonly seen (and never abundant) in the salty water of bays and estuaries. In contrast, water-rats are known to inhabit ocean beaches and are found on many islands surrounded by sea water.
Platypus are dark brown in colour, with lighter underparts and a small white patch located next to each eye. Similarly, water-rat fur usually looks dark brown when the animals are wet. When water-rats are dry and seen at close range, their fur may (depending on the area) be chocolate brown, reddish brown, mouse grey or even mottled grey-brown, with underparts that vary in colour from cream to light brown to golden yellow.
Both species typically float low in the water, with just the top of the head and back (and sometimes a bit of tail) visible as they swim on the surface.
Platypus and water-rats are also quite similar in size, with adult males of both species measuring up to about 60 centimetres in length (including the tail). Juveniles are of course smaller than most adults when they first enter the water.
Juvenile platypus first emerge from nesting burrows in late January to early March in Victoria and New South Wales. Queensland juveniles emerge a few weeks earlier and Tasmanian juveniles up to around two months later. By comparison, young water-rats are seen over a much longer period of time, from early spring to at least early autumn.
The best way to distinguish a water-rat from a platypus in the water is to look carefully at the tail. The water-rat has a long, narrow tail with a conspicuous white tip, whereas the platypus has a flat, uniformly dark, paddle-like tail. Platypus are also very rarely seen on land, though they may occasionally rest on a log or rock, usually while grooming.
Visit this site for more information on platypus swimming and diving behaviour.