How ironic, just last night while I and my training partner did a little open water swimming practice this very topic came up. There have been several 'gator sightings in North Texas, and the thought went that mass starts aren't a concern, individual training is more likely to draw a 'gators interest. I really don't want to be a meal...
I am in Florida too. I do lots of triathlons in lakes. Most of the time I don't give it a second thought. The only one that gave me pause was Longleaf last year, which was in a "lake" that was more like a pond. It was a time trial start so there was no protection from a pack of other people. And before the race they drove a jet ski around the lake to scare the alligators. Plus the water was as dark as coffee, which is usually the case with FL lakes.
I'm doing the race again, though. Not really worried about it.
I compete in Central Florida (Orlando) and haven't had any concerns until recently. I've done a few races (have one tomorrow morning) since all the media coverage on the topic, but there hasn't been a problem. If I let my fears dictate what I will and will not do, I might never do anything I really want to do.