We are travelling to Lake Garda and Venice for 11 days in June. We fly into Venice and will then travel to Lake Garda. We plan to take the bus to Mestre and the train to Pescheira Del Garda, bus to Bardolino ( reverse trip 7 days later). Do we need to book the train?, I have so far looked on the Trenitalia website but keep getting the message "one or more section of this trip is not bookable", am I missing something? We would be grateful for help with all or any parts of the trip, thanks.

It is likely an R train[ regional] and is not bookable--just buy it that day. Why bus to Mestre---the same train may start in Venice.

Trains leave Venezia SL (Santa Lucia, the main Venice train station every 10 minutes or so all day long). Most of them make their first stop 7 minutes later in Venezia Mestre. As Bob wrote, you may be able to take the train all the way.

To explore options, use a date within the next week on the Trenitalia site. The schedule for this type of train (R) is not shown that far ahead.

Thanks for the info., very helpful. sorry if I wasn't clear, we are flying into Marco Polo and travelling onto Bardolino for 7 nights, then back to Venice for 4nights, so bus is from Marco Polo to the train station, thought Mestre may be easier.

And you are correct !