It's awkward, swimming in the Serpentine! (5)
I believe the answer is:
inept
'it's awkward' is the definition.
(synonyms)
'swimming in the serpentine' is the wordplay.
I cannot quite understand how this works, but
'in' is found in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for inept that I've seen before include "Incompetent or gauche" , "Hopeless; bungling" , "Not competent" , "Showing a lack of competence" , "Unsuitable, clumsy" .)