I always try to keep an eye on my surroundings when working on lakes, but sometimes you just forget.
About seven years ago I was mowing a lawn on a large lake and regularly saw a 7.5-8' alligator patrolling the shore line. As I would get to the lakeside he would move out about 30 or 40 feet and resurface. I always kind of knew it was around, but was pretty easy to keep track of.
But one late afternoon I got in a big hurry and was trying to get the place done. The first thing I did was go down to the shoreline to pick up some tree limbs. I never even thought about the alligator. I had my back to the lake bending over to pick the stuff up. Now remember, this is late afternoon. I saw a long shadow and a split second later a loud splash. It was sitting right there and I never saw it. The shadow was it flipping itself backwards with it's tail to head out into the lake. Scared the &*$# out of me