Background: Rowing is a sport that places significant stress on the lower back, often leading to low back pain (LBP) injuries among athletes. Laboratory studies have shown that rowing with an oar blade under an angle is more efficient compared to a traditional blade. The effect of blade angle on the lower back is unknown. Therefore, the aim of this study is to investigate the effect of different oar blade angles on the muscle activation of the lower back muscles during on-water rowing. Methods: Seven collegiate (five males, two females) athletes row 500 m on water twice, once with a traditional (0-degrees blade) and once with an oar blade under a 5-degrees angle. Surface electromyography of the longissimus muscle of the erector spinae was measured bilaterally at the thoracic and lumbar level with a sample frequency of 2,000 Hz. In total 1,443 strokes were analyzed. Statistical Parametric Mapping was used to investigate the differences in muscle activity between the 0-degrees and 5-degrees oar blade. Results: No significant differences in muscle activity were found between the 0- and 5-degrees oar blade. Conclusion: Rowing with an oar blade under 5-degrees did not alter the muscle activity during on-water rowing. This indicates that rowing with an oar blade under 5-degrees may not increase the muscle activation. These results are important as it seems that a change in oar blade angle does not increase the injury risk, longitudinal studies should investigate the effect of oar blade angles on LBP injuries.