Quick update - Just found this and thought I should pass along.
"In summer (from May 31 to September 30) is available the direct line of transportation "Clodia" by boat (vaporetti) with departures from stop Venice-Pietà (the stop is located in front of the omonim church, unique departure at 5pm); the same vaporetto, towards Venice, leaves from Isola dell'Unione at 9,05am and Piazzetta Vigo at 9,15am.