Witness reported small bear being seen underwater (3,4)

I believe the answer is:

sea slug

I'm a little stuck... Click here to teach me more about this clue!

'seen underwater' is the definition.
I can't tell whether this defines the answer.

'witness reported small bear' is the wordplay.
'witness' becomes 'see' (synonyms).
'reported' indicates a 'sounds like' (homophone) clue.
'small bear' becomes 'slug' (I can't explain this - if you can you should believe this answer much more).
'see' sounds like 'sea'.
'sea'+'slug'='SEA-SLUG'

'being' is the link.

Can you help me to learn more?

(Other definitions for sea slug that I've seen before include "Creature" , "Shell-less marine mollusc" , "gastropod mollusc" .)

I've seen this clue in The Telegraph.

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.