Why do backswimmers swim upside down?

Backswimmers (family Notonectidae) swim in an inverted position because they store their supply of air in bubbles trapped under hairs on the underside of their abdomen. By swimming upside down, they keep this essential air supply positioned correctly for respiration while submerged.12

This orientation also aids in their survival through countershading. Their light-colored backs, when viewed from below, blend into the water surface and sky, while the darker rest of their body blends with the bottom of the water when viewed from above.1