Is the lake managed by any government entity? Transport Canada manages most waterways and where my place is in Ontario the township has some jurisdiction as well. It would take a lot of political interference to make such a massive change.
Waterways are public entities, anyone can access them. Since you have property on the water, assuming you can launch your boat, there's not much anyone can do to stop you.
The ski course is a seperate issue, I was told by transport Canada that if the lake owners association doesn't want the course, it needs to be removed, even if you have a permit, baring major legal battles...
Yes you need to organize. Go to every homeowner who has a boat... Be nice 🙂