I've had water moccasins actively chase me...those things mean business!
Almost felt bad when I was untangling him from the end of my trimmer.
I have had an 8 foot gator follow me up and down a 500' bank once though.
It was swimming about 3 feet off the shore. I tried scaring it away with my trimmer (hitting the water with it) he/she just went under water for a second, and came right back up and kept following me.
I did the sloppiest lake bank ever that day, it's hard not to scalp it when you are staring at the dinosaur that is either curious or potentially wants to eat you.
Called FWC after that job and let them know of a potentially aggressive gator, the next day the client called me up and told me "three large men from the state came and wrestled it into the back of a pickup truck"