The secret is to watch their hind legs. If the gator has the rear legs tucked underneath them, watch out! However, if they have them splayed to the sides, they are pretty much resting and want to be left alone.
They usually pull in their hind legs a bit slowly, but if you're watching you can usually back off out of leaping range before they whip around.
I wouldn't go anywhere in the water though. Alligators can move like the wind in water!
Yeah, the whipping around is what I would have been concerned with. And he looks like he's watching everything you are doing, and getting ready to move if you go to his right side. Interesting about the back legs. I see what you mean. Still, yikes.