The sewer rat is the miner of the rodent family. They are often found in colder climates and are famous in New York.
They are larger than the roof rat and gregarious, meaning they don't mind meeting you. Commonly these rats come up from the sewer where they are present in high numbers. When above ground, they are live in borrows. Burrows have more than one entrance to them. When occupied the rats often excavate fresh dirt out of one of the entrances, producing evidence the burrow is currently in use. Burrows sometimes collapse resulting in oval depressions in the ground.
Being a the largest of the rodents in New Zealand and often in high numbers commonly they have a strong offensive odour where they live.