you don't need a boat to get up there. If you have a sled it's around 16km up a logging road (from Taghum) to the bottom of the course. If you don't have a sled, it's about a 8 or 9km skin up (from 6 mile) to the top of the ridge across the drainage from the course.
Not easy to get to, but you definitely do not need a boat. How do you think those logging trucks get in in the summer?
Even though practically all cat/heli operations are on crown land, meaning the public is allowed to use them at any time, most operations and locals have an unspoken agreement along the lines of: When the operation is, well, operating, the sledders stay out of their terrain. This is more important in certain places (like Big Red Cats, Retallack, and Wildhorse) because they are pretty much right on the side of the highway.
Valhalla Powdercats had an issue years ago because they had their first tenure in a very popular sledding (and sled accessed skiing) zone in the area. The two sides couldn't agree, leading to road blocks and threats of violence. This resulted in Valhalla Powdercats having to move to a new location deeper in the Valhalla Range and a restraining order against certain members of the community. In the end though, mostly everyone got what they wanted.