Water temperatures in estuaries along the NSW coastline have warmed more than 2 degrees over the past 12 years and the water has become more acidic, according to findings that are likely to be mirrored elsewhere in Australia and similar temperate zones.

Researchers used data collected by the NSW government on 166 estuaries and similar water bodies along 1100 kilometres of the coast to track changes over the period up to 2019. The results were published in the Nature Communications journal on Tuesday.

Estuaries along the NSW coast are warming much faster than the air and ocean, and turning more acidic, a new study has found. Credit:Nick Moir

While scientists had looked at trends in individual estuaries such as the Hudson River in New York or Chesapeake Bay near Washington, how large regions were changing was "a question that hadn’t been answered anywhere around the world”, said Elliot Scanes, a marine biologist at the University of Sydney.

Dr Scanes - who worked with the university's Professor Pauline Ross and his father Peter Scanes from the NSW government - said "the rate of change is one of the most surprising aspects of this study”.