Hi cading
Thank you for your question.
The SwissPass is only an “empty” card: what counts is what kind of travelcard you charge on it.
If you have a GA travelcard, journeys by boat on the Brienzersee are included.
Find here a map with the validity areas of a GA travelcard: Summary of all GA Travelcards on the SwissPass | SBB
If you ave any other kind of travelcard, please call our colleagues at the SBB Contact Center (+41 848 44 66 88, CHF 0.08/min) to check the validity.
Kind regards
EleonoraS