The Sydney desalination plant's biggest effect on the nearby ocean is unlikely to be from the release of toxic saline brine, in an unexpected outcome from what is claimed to be the world's first peer-reviewed study into the industry's marine impacts.

The report, published in Water Research this month, found the $2 billion plant had a negligible effect on the offshore ecosystems during the two years it was operating before its mothballing in mid-2012.

A rock cod and other fish at the inlet point of the Sydney desalination plant. Credit:UNSW

“We’re fortunate and relieved that the ecological impacts are minor compared to what people thought might have happened with this development," said Emma Johnston, a professor of marine ecology at the University of NSW and a senior author of the six-year study.

That result is heartening given that about 1 per cent of the world's population are already dependent on 20,000 desalination plants. Demand is expected to soar as water scarcity worsens with climate change and rising usage.