Productivity of Gavia immer (Common Loon) has declined in Ontario and across southern Canada. Variations in the timing of lake ice-off have the potential to negatively influence productivity of Common Loons, but there is conflicting evidence as to how ice-off dates affect this species' reproductive success. Our study investigated the association between annual ice-off timing in southern Ontario and the presence and reproductive success of Common Loons surveyed at 69 small lakes in 16 years over a 38-year span (1982–2019). We found negative relationships between residual ice-off date and the presence of Common Loon pairs, the proportion of Common Loon pairs attempting to breed, and the number of large young per pair per year, suggesting that there were fewer pairs, breeding attempts per pair, and large young per pair in years with later ice-off dates. Our results show that ice-off date is an important factor affecting reproduction in Common Loons, and that ice-off dates can be used to help predict annual variations in productivity of Common Loons.