The news this week in Charleston is about a man who lost his arm to an alligator while scuba diving in one of the large lakes near the city. For a gruesome photo of this event you can follow this link. (Yes, that is a human arm!). I don't think that many of us who live in the southeastern US need to be reminded that dogs and alligators don't mix well.
Labradors like to swim and having your dog retrieve in a waterbody that hasn't been checked for large toothy reptiles isn't healthy for the dog. I did a biological study of impoundments in the Santee Delta where there were on average 60 alligators per 6-10 acres of impoundment. The work required wading into the impoundments and nearby creek. We were always cautious when doing our work because of the alligator population. Now, I'm glad that I got the work done, the paper published, and don't have to go in alligator infested waters anymore.
Generally, one can't be certain what ponds and other water bodies in the Charleston area have alligators in them. It's best if you don't know the pond, to not send your dog into the water. Even a 6 foot alligator can easily grab and drown a 75 lb. Labrador. I don't even want to think about the Big Boys that are lurking about.