Swimmer enveloped in surf is happy (4)

I believe the answer is:

fish

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

'swimmer' is the definition.
(fish swim)

'in surf is happy' is the wordplay.
'in' indicates a hidden word.
'FISH' is hidden within 'surf is happy'.

'enveloped' is the link.
I am not very happy about this link. It may belong to another bit of the clue.

Can you help me to learn more?

(Other definitions for fish that I've seen before include "Aquatic vertebrate" , "To try to catch" , "Swimmer" , "Aquatic animal(s)" , "Aquatic creature(s)" .)

I've seen this clue in The Times.

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