The European Otter is part of the Mustelidae family. It is well adapted to aquatic life. Its sleek fur is water proof. This animal has interdigital membranes and it can close its mouth and ears as long as it stays under the water. It is a mid-sized mammal and it can reach the length of 1, 30 m, with a weight of 12 kg. 

The Danube's Delta is an ideal habitat for the otter population in the area. The otter builds its burrow in the shores covered in vegetation. Their burrow has a complicated design, with secret entrances. One of these entrances is always under water.

The European Otter swims with its entire body and its tail, using tortuous moves. The only time when it uses its legs is when it changes direction. Its mating season is not well defined, but during mating rituals, males become aggressive. They will fight for territories and females. The female will give birth to 2 or 3 cubs. After a month, they will be able to see. The female will take care of the cubs by herself.

For many years, the European Otter used to be hunted for its fur, but also due to the damages it made in fish ponds.

Currently, the European Otter is protected by international conventions and in some EU states the damages made by it are compensated.