Swimmer feeling about (3)
I believe the answer is:
eel
'swimmer' is the definition.
(eel is a type of fish)
'feeling about' is the wordplay.
'about' indicates a hidden word (the clue goes around or about the answer).
'EEL' is hidden within 'feeling'.
(Other definitions for eel that I've seen before include "Serpentine fish" , "Large elver" , "elusive person" , "A sea snake" , "Long thin fish" .)