While growing up and living in the rural South, we did consider snappers and "tarpins" (Southern for terrapins) as varmints in the local ponds and small water sheds. Old ponds and bass/bream/catfish lakes were often infested with younger, and sometimes, old snappers that wreaked havoc on fish populations, ducks, etc, and were a general nuisance by stealing bait off lines.
In the spring when these varmints were sunning on numerous logs, stumps, mud banks, etc, a friend and I found a new sport in attempting to control these creatures. Most of these ponds, lakes and sloughs were very rural and offered plenty of shooting angles that allowed safe zones for any water ricochets. Typically, we used 22LR for these varmint control shoots, and usually, the ranges were 200yds +/- and under to a few feet. Once a small lake or pond had been shot a while, the wiser "tarpins" would instantly go to water upon seeing us on the banks or levees. These called for longer range shooting with 222's, 223's etc.
The real challenges came when the springtime waters warmed enough for the turtles to stay in the water for long periods and only presented head shots to our 22LR's.
Occasionally, we would get a bonus and find cotton mouth snakes lying on these same logs and stumps sunning in the spring sun while out of the still rather cold waters. And more than once, we would be surprised by a rather extremely large female cotton mouth who lazily slithered onto a log or mud bank while we were sniping the turtles. A couple of those we retrieved after shooting were so large, they gave me a cold chill down my young spine. But, they made great belts!