Waitoreke is a creature equal to black rat in size, but much more graceful. This rodent is the descendant of black rat introduced to New Zealand by ancestors of Maori – aboriginals of archipelago. Waitoreke is named after certain river animal (“otter”) of local legends. In many respects it resembles this animal which remained a mystery for official science. The wool of waitoreke is colored grey tone: back and head are dark grey, and the bottom part of body is ash-grey. The tail of waitoreke is black, flattened, covered with hairless skin, resembling beaver tail in outlines. Forepaws are shorter then rear legs and have well advanced fingers. Around of eyes of mammal there are white “glasses”. Its muzzle resembles muzzle of rat, with well advanced vibrissa. With the help of vibrissa touches this animal can search for food even in muddy water. Eyes of waitoreke are large, and ears are small, rounded and almost unnoticeable in wool. Waitoreke is skillful fisher, and this fact has leaved a mark on its appearance: this little mammal has small ears, strong webby hind legs and waterproof fur like an otter. Secretions of special glands give to waitoreke’s fur necessary water-repellent properties. Due to greasing the animal gets out of water almost dry – it needs only to shake some drops of water from itself. Such adaptation helps this animal to keep heat even at life in cold mountain lakes and streams. The special valve closes an acoustic duct when animal dives. This little mammal lives in coastal zone of rivers, streams, lakes of both islands of New Zealand. Waitoreke prefers to live in woody area, but also settles in plain areas. It eats various aquatic animals: snails, frogs, aquatic insects and fishes. Sometimes waitoreke catches nestlings of waterfowl, snatching them from under water or stealing from nests. Animal catches prey by forepaws and kills by bite of strong incisors. Waitoreke hunts large fishes in packs. Waitorekes live in rallied colonies resembling a colony of meerkats. The colony represents some tens of holes dug near to water edge of reservoir. In each hole one couple of adult beasts lives. One couple is dominant – their hole is located in the center of colony, and at lack of forage dominants can take food away at other animals of a colony. But at danger the dominants attack enemy the first. When in the morning all animals go to the search of food, some “sentinels” stay in colony. They notify relatives on danger by loud whistle, and if necessary, protect cubs actively. The enemy of waitoreke is antipods’ unotter (Xenolutra antipodorum) which lives in a lower reaches of New Zealand rivers. Herons and large predatory fishes, and also neohanasaki (Neohanasaki aotearoae), large species of amphibians, may eat adult animals and cubs. These animals form pairs to all further life. Courtship period at waitoreke takes place in spring (October in Southern Hemisphere), and posterity is born in the beginning of summer. The second litter is born at the end of summer. In spring litter of this animal numbers up to five cubs though usually it is less, in summer – no more than three ones. Cubs are born at all couples capable to breed, and not just at the dominant couple. However in dominant’s litter cubs are larger, and on the average, the litter numbers one cub more, than at other couples. Young animals become sexually mature at the age of 6 – 7 months. At this time young animals leave parental colony and form their own colony, or join one of existing waitoreke colonies.