Internet-tough-guy violent fantasies aside, your plan as a couple of flaws.
First of all, a snail darter
is a fish, and DDT
is an insecticide. (Looks like your knowledge of biology and chemistry is right up there with your knowledge of climatology.) As hilarious as it would be to watch a bunch of rednecks stomping around in a riverbed and using insecticide to try to kill a fish, it's probably not the most effective method to achieve your goal.
Secondly, lefty liberal loons are a wily bunch. They would probably be crafty enough to plan their protest on a day when Larry the Cable Guy was in town or McDonald's reintroduced the McRib. So your "minions" would be otherwise occupied.
But I will give your plan points for theatricality. It's runs the gamut from insanely stupid ("Let's go stomp some fish!") to just insane ("Let's poison an entire ecosystem!"). I've never seen something so filled with hateful crazy that wasn't a plot to kill James Bond.