I think that if you were just floating in the water around an airport, at least in the U.S., you would probably be approached by law enforcement, they might not do anything but I would bet that someone would stop by. I could only imagine the shots you could get at like SFO
. But, I have noticed that they have gotten very curious about people hanging out around the airport since 9/11. It has been mostly just a "hello" and not asking you to leave or anything.
One mile of highway gets you one mile, one mile of runway gets you anywhere.