Translation:I do not swim in September.
What about "I am not swimming in September!"
It is equally correct.
Specialmente non a Canada dove può nevicare a volte a settembre!
Since month ranges seem to be expressed in Italian (as in Spanish, Portuguese, and French) using "a" -- e.g., "da maggio a luglio" -- I almost said "I do not swim until September." Would that be "...fino a settembre"?