When the girl with the shotgun tries to shoot the clay pigeon she accidentally shoots the line towing the para sail and the line clearly separates. As the sail into the lake you can see that the cable is still attached to the boat.
The opening scene well-establishes that this bus driver drives to the camp regularly, likely every single session/year (so regularly that both her and the camp director count on her arriving at the right time to the second). Yet the old camp sign is too low for her bus and gets knocked down from age and the impact. Her bus appears to be a standard bus of a standard height, so any bus would do this. If she's been coming here for multiple seasons, the issue of the sign being too low would have been discovered and fixed years ago (or else it would have been knocked down as the movie depicts years ago).