It is difficult to catch a glimpse, but with patience and silence, we may be able to watch its wanderings on a quiet stretch of water in the early morning or late afternoon.

It is a medium-sized carnivorous mammal, with mainly nocturnal habits and perfectly adapted to the aquatic environment.  It can reach a total length of 1.20 m, with a dense coat (regularly lubricated and waterproofed with a fat that it secretes from glands) and a long, muscular tail. It has short legs with skin between the toes, which allows it to swim quickly and efficiently. Its long whiskers enable it to locate its prey with precision, which it then catches underwater.  The ears and nostrils have an ingenious system that automatically closes them each time it dives. It can stay underwater for up to eight minutes.

Alt feeds mainly on fish. But in watercourses where the Red Crayfish is present, it certainly prefers this freshwater invader. Its diet also includes amphibiansand some waterfowl.

It is an endangered species at the European level, mainly due to pollution and loss of aquatic habitats.