Rattus lutreolus is the Swamp Rat. There are plenty of Swamp rats around the outer urban areas East of Melbourne. They are native to the area. They are not related to Black or Brown rats, which are the real "vermin".
The Swamp Rat can be seen at places like the Healesville Sanctuary, where they wander at will around the grounds, feeding, exploring and doing their rattie thing. The rangers at Healsville have no problem with them wandering around, since they are native to the area and carry no dangerous diseases. The only problem would be if visitors fed them too many treats and they became overweight.
