Damselflies are four-winged, joint-legged, carnivorous arthropods in the class Insecta. They hatch from eggs laid in still water bodies (only a few of our North American damselflies lay eggs in fast water) and hatch out into the larva shown in the photo. This particular damselfly larva was about 2 cm in length. The "gills" are the three large feathery appendages on the end of the abdomen. They live underwater for 1-3 years (depending upon species, latitude, and water temperatures before emerging and spending the rest of their life as free-flying adults.
This particular damselfly larva was found in a large pond in a wetland complex in northwest Wisconsin.
I've done some research on damselflies, but haven't been able to narrow the ID other than being able to identify this specimen as a damselfly.