These guys have strong legs set back far on the body, which gives them extra strength in propelling them underneath the water during dives. It also makes them fast swimmers above water, as evidenced by the bow wake seen here.
Canon 7DII + 500mm f/4 II + 1.4TC III, manual exposure, evaluative metering, 1/1250s., f/6.3 (I must have accidentally bumped the aperture down by one click), ISO 800, natural light, handheld, small crop for comp, a few bits of debris removed from the water.