Easiest swimming round island, in my opinion (2,1,3,2)
I believe the answer is:
as i see it
'in my opinion' is the definition.
(both might be said before giving an opinion)
'easiest swimming round island' is the wordplay.
'swimming' is an anagram indicator.
'round' means one lot of letters goes inside another.
'island' becomes 'i' (geographical abbreviation).
'easiest' is an anagram of 'asiseet'.
'asiseet' enclosing 'i' is 'AS I SEE IT'.
(Other definitions for as i see it that I've seen before include "IMO" , "In my judgement" , "in my view" , "In my opinion" .)