Line is circling party venues supporting swimming (5)
I believe the answer is:
lidos
'venues supporting swimming' is the definition.
(type of swimming pool)
'line is circling party' is the wordplay.
I cannot really understand how this works, but
'line' could be 'l' (used when specifying particular lines from a poem) and 'l' is found within the answer.
'party' could be 'do' (do is a kind of party) and 'do' is located in the answer.
'is' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
(Other definitions for lidos that I've seen before include "bathing beaches" , "Open air swimming pools" , "Solid (anag) -- pools" , "swimmers like them" , "which swimmers may use" .)