Eurasian Otter

The Eurasian otter, also called the European otter or common otter, is a semiaquatic mammal and the most widely distributed member of the otter subfamily (Lutrinae), found in the waterways and on the coasts of Europe, much of Asia and parts of North Africa. It eats mainly fish and is strongly territorial (Wikipedia, general species account).

It is endangered in some parts of its range but recovering in others. The source used here is a general species account and does not cover the species on Sumatra, so its local status there is unconfirmed.