Leading magazines for upcoming Venice festivals and events are regularly published and there are weekly event guides that are readily available.

Venice Events in September -

Regatta Storica - first Sunday in September, this historic gondola race first took place in 1274 and starts at Castello
Vivaldi Festival - this is a popular festival of contemporary music

Venice Events in October -

Venice Marathon - first weekend, this race is enjoyed by crowds of spectators

Venice Events in November -

VeniceSt. Martin's Day - a popular fair in the streets of the city
Festa della Madonna della Salute - 21st November, this procession over a bridge of boats across the Grand Canal to the Basilica di Santa Maria della Salute gives thanks for the end of the great plague in 1631