While carefully raised domestic otters are in general not aggressive, they are very playful and even their play bites can be hurting if they get a bit too carried away in the play. But the same applies to cats, dogs and other domestic animals.
Usually otters like most wild animals are quite shy, but otters are also very curious creatures and despite their cuteness they are ferocious little predators.
So the rule of thumb is: if you encounter wild otters, keep the distance and stay calm, so they won’t get nervous or feel attacked or cornered.
Don’t disturb them when they eat or having pubs, this automatically puts them in defense mode.