Notonecta spp. / True Bug Family (Heteroptera)
Backswimmers are aquatic insects, as their common name attests, they swim upside-down. Being true bugs, they have piercing mouthparts and can bite if handled. The long rear legs are used like oars. They keep their abdomen in contact with the surface of the water in order to breathe.
This photo was taken through the surface of the water with a telephoto lens and cropped heavily, so it is not the best quality!