Speaking of the rivers here. The St. Johns seems as if it's fed from the Atlantic? It seems like it is only "fed" by the ocean. Or does it have some source that pushes it both out to ocean and down our way? Even if it isn't fed that way and for some reason it's a magical river that flows north, then it would still be a slightly brackish salt-water mix in the "lower" river basin (in the North end of the river, in this magic backwards river scenario). Can mosquitoes live in salt water? I would think it would make the larvae dry out.
