What about Lac des Arcs? I used to see motorcycles on there all the time.
I thought that Ghost Lake was part of a provincial park, so wouldn't use of a park be up to the province to decide and enforce? I also thought that a property owner can't prevent anyone from using waterways unless it is a private lake (that is, a lake where they own the entire shoreline, which in this case they don't). So does trans-alta really have the rights to restrict how the lake gets used?
Third option... Have SASC accept all responsibilities for its own actions (in writing to TA) so that TA's fears of liability are unfounded.