I identified this as Notonecta kirbyi (see U of A Entomology Collection
). N. kirbyi is larger (12-15 mm) than N. undulata, the other coexisting notonectid species in south Alberta. N. kirbyi also has a pair of dark broad cloudy bands on the hemielytra as seen in this specimen. N. kirbyi also has a bare keel that is hairy on both sides on abdominal sternite 4 (not shown in the image).