As both are often found living near water, and both to me look very similar, how can you tell the difference between otter and mink? Very similar looking creatures but completely different personalities!

Mink are half the size of an otter, and have more pointed heads than an Otter. Generally they are darker furred and face has a rat like appearance, unlike the rounder face of an otter

When you see them both they are very different looking animals. The Mink is about the same size as a cat, the Otter around twice the size. The Mink's tail is bushy like a fox's' the Otters tail more resembles that of a Rat but relatively shorter.

otter poo or spraints supposedly smell of jasmine tea and are usually full of fish bone
mink poo smells bad