User blog comment:ChishioKunrin/Volume 6 Bingo/@comment-4141313-20180807135123/@comment-4010415-20180808065243

Oddly, we didn't see any signs of boats in that huge lake. I wonder if there's a reason for that. Maybe the locals just prefer not to take a boat out onto that lake because one sting from a Lancer would sink it?

I suppose one explanation they could provide, if they actually dwell hard enough on the subject to think of it, is that Mistral temporarily shuts down air travel while they search for any remaining White Fang members that might be in the area, as air travel would make it quicker and easier for the lurking White Fang members to get away. Ozpin insists on getting to Atlas as soon as possible and doesn't want to wait for Mistral's search operation to finish, so RNJRWBY just goes ahead and walks out through a checkpoint.