evidence: Across 166 Australian estuaries over the last 12 years, the summer estuary water temperature increased on average by 2.16 °C (0.2 °C year−1), pH decreased by ~0.5 pH units and salinity decreased slightly (mean −0.97, −0.086 PSU year−1). Australian air and sea temperatures have increased by ~1 °C since 191021; however, eastern Australia is warming faster than the rest of the continent. Over the last decade, summer air temperatures in eastern Australia have generally increased by 1.5 °C, and sea surface temperatures have increased by ~1 °C compared with the 1961–1990 average20. Our findings show that overall, estuaries are warming generally faster than these temperatures, with much of the warming concentrated in lagoons and rivers, with less change in lakes and creeks. Previous work has shown that small inland creeks22 and large riverine estuaries6,8,9 follow the trend of air temperature. Our results suggest that this may hold true for some estuaries; however, the drivers of change are complex, and the factors affecting the degree of warming in estuaries are more than just air or ocean temperature.