Australia is being urged to accelerate its efforts in rescuing the Great Barrier Reef amid fears the nation will fail to meet its 2050 target.
The Reef 2050 Plan was released by the Australian and Queensland governments in March 2015 to protect and manage the reef, which is at risk of being placed on UNESCO's "danger list".
In a report released in Paris on Saturday, UNESCO praised progress in the inception and initial implementation of the rescue plan but voiced "serious concern" over the scale of mass bleaching to the reef.
"Progress towards achieving water quality targets has been slow and the most immediate water quality targets ... are not expected to be achieved within the foreseen time frame," the UNESCO report said.
A previous report revealed coral bleaching at the Reef in 2016 was even worse than expected with the most severe bleaching found north of Port Douglas.
There, an estimated 70 per cent of shallow water corals had died along with significant variability between and within reefs.
It's now confirmed about 29 per cent of shallow water corals died from bleaching during 2016, up from the previous estimate of 22 per cent.
UNESCO, which advises the World Heritage Committee, said greater work surrounding water quality will need to be accelerated if the immediate and long-term targets are to be met.
The report named climate change as the "most significant overall threat" to the reef and said the scale of bleaching in 2016 was an important insight into the "severity of the threat".
WWF-Australia Head of Oceans Richard Leck said Australia must urgently boost efforts to clean up pollution from Reef catchments.
"Two years ago UNESCO put Australia on probation until the health of the Reef improves. Clearly that probation is not going well," Mr Leck said on Saturday.
"Since then there has been an unprecedented loss of coral.
"Never has more urgency and leadership been needed to make sure the Reef is not lost on our watch."
