This is obviously not living in the water, as it is hanging out on a pine tree, but before young dragonflies transform into adults, they live in the water and prey upon other invertebrates and even small fish or tadpoles. This adult was found not far away from the pond/lake where the rest of the pictures in this post were taken. It is most likely Ladona deplanata, aka a Blue Corporal. Yes, I know that it's not blue, but this is most likely a female, which are a different color. Pictures of males and other females here http://bugguide.net/node/view/27364/bgimage
This is a carnivorous sundew (genus Drosera and most likely D. brevifolia), which I've posted other pictures of, that is about to flower. There is a picture here http://www.florida.plantatlas.usf.edu/plantimage/Drosera_brevifolia5.jpg of what it may look like when it flowers.
These are some ants, most likely fire ants (Solenopsis invicta) that were flooded out of their nest. They floated on the water and gathered together and are now clinging to a plant that sticks out of the water in hopes that the water goes back down.
This is a young backswimmer (family Notonectidae) that is just under the surface of the water in a pond/lake in sandhill habitat. Sandhill habitat is xeric (meaning very dry and pronounced as if the x were a z), but there are temporary and permanent wetlands in some sandhills. I think that you can see why it's called a backswimmer. It swims well and its long back legs are kind of like oars on a boat. It eats other insects and invertebrates.