Some idiot terrified a swimmer (5)

I believe the answer is:

otter

(Other definitions for otter that I've seen before include "Riverine mammal" , "Playful aquatic animal of 'Tarka' fame" , "Fur possibly" , "Holt dweller" , "Carnivorous aquatic mammal" .)

I've seen this clue in The Sun.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.