Performing a trio around a lake (7)
I believe the answer is:
ontario
'lake' is the definition.
(I've seen this in another clue)
'performing a trio around a' is the wordplay.
'performing' becomes 'on' (as in being on stage).
'around' means one lot of letters goes inside another.
'trio' going around 'a' is 'tario'.
'on'+'tario'='ONTARIO'
(Other definitions for ontario that I've seen before include "Canadian province and Great Lake" , "Most populous Canadian province" , "part of Canada" , "Province of SE Canada, and a Great Lake" , "Oration in Canadian province" .)