Jun 7, 2014 - 5:47 PM
in reply to Wineycat
Late May/early June is indeed too early for the higher trails, but all others ones are open around that time. July through September is the best time. Early October is usually fine too. Late October, the chance of snow at the higher altitudes is increasing. There is no fixed date for trails to close, as this is weather dependent. There's only a fixed closing date for cable cars/funiculars etc. Although exceptional weather can sometimes cause early closure or late opening as well.
The boats on Lake Thun operate all year round (although in Winter very limited), on Lake Brienz there are no boats in Winter. Links to the timetables can be found on the pages I linked to.