This event has been bugged for months now. Typically the NPCs are stuck on the lake shore. I have camped the area and it does not happen. I am aware of the event cycle from the time before it became broken.
I have reported it many times via the bug report option but I am convinced that no-one actually takes any notice at all of bug reports. I have reported 100s of errors, without an exception, they are still present.
I doubt very much if reporting here will do any good but I am excessively optimistic by nature.