The otter (Lutra lutra) is a weasel family species that has adapted to aquatic life. It enjoys living on the shores of both large and small waterways and especially in the autumn and winter time otters will visit Myllylähde. Its only environmental requirement is that there are enough fish to catch in the water. It is one of the larger animals in its family and can weigh up to 12 kg. It has a broad snout and its paws are adapted to aquatic life.
Its diet consists mostly of fish, but also includes small mammals, birds and frogs. A full-grown otter will eat up to a kilo of fish per day for food. If the catch is abundant, the otter will store it. In the opinion of fish farmers, otters can be a problem due to their ability to store food. However, the fish stocks in natural waters do not significantly decrease as its catchment area is generally quite wide. If fish stocks become depleted and catching fish becomes difficult, otters move to other waters. An otter can move more than ten kilometres a day and it also moves effortlessly on land when moving from one watercourse to another.
The otter becomes able to reproduce as a three-year-old. Mating usually takes place early in spring. However, the species may come into heat at almost any time of the season, but the young are usually born at the beginning of the summer. The otter’s love life is short though as the male leaves the female after mating. The female makes a sheltered cavity in its den (holt) where it gives birth to two to four young. At the age of two months, they leave the holt in the company of their mother and remain by her side for about one and a half years
The otter has spread over almost all of Finland. In Southwest Finland, South Ostrobothnia and the shores of the Gulf of Finland, the species has long been very rare, but at this moment the population is growing rapidly. Thus, it is returning to its former numbers – it was once a very common sight at the beginning of the last century. However, it was hunted for its valuable coat and almost become extinct in Finland until it was granted protected animal status in 1938. Thereafter, there has been a steady rise in the population, although it has been hunted to a limited amount. Today, it is protected throughout the year. Before it became a protected species, it was hunted vigorously but today the worst threat to it are ecologic problems, such as the pollution of the waterways and human population spread. In Southwest Finland, the species is limited by the scarcity of rivers and the lack of water.