Unesco has expressed “serious concern” about the impact of coral bleaching on the Great Barrier Reef and warned Australia it will not meet the targets of the Reef 2050 report without considerable work to improve water quality.

The criticism was contained in a draft decision published as part of the agenda for the upcoming world heritage committee meeting (pdf), which will take place in Krakow, Poland, in the first two weeks of July.

It suggested the Great Barrier Reef should remain off the danger list, despite back-to-back coral bleaching events affecting about two-thirds of the reef and the latest data showing a sharp decline in coral cover in the north.

The draft decision also praised the Australian and Queensland governments for initial work done to implement the Reef 2050 plan that included establishing a $1.28bn investment strategy, most of which will be spent on improving water quality.

However, the report said progress on reducing the number of agricultural pollutants flowing into the reef “had been slow” and Australia would not, at this rate, meet either its interim or long-term targets to improve water quality.

It “strongly encouraged” Australia to “accelerate efforts to ensure meeting the immediate and long-term targets of the plan, which are essential to the overall resilience of the property, in particularly regarding water quality”.

It also said climate change remained “the most significant overall threat” to the future of the reef, and “recommended that the committee express its serious concern at the coral bleaching and mortality that occurred in 2016 and at the second event underway in early 2017.

“While the long-term effects of these events cannot be fully evaluated yet, their scale serves to underline the severity of the threat to the property from climate change,” Unesco said. “At the site level, there is a need to consider how these mass bleaching events influence the effectiveness of the [Reef 2050 Long-Term Sustainability Plan] in its current form, notably in relation to the most urgently needed measures and improvements that contribute to the property’s resilience.”

Meeting those water quality targets would require a ten-fold increase in investment to $10bn over the next 10 years, the leading expert on water quality for the reef, Jon Brodie, said.

It would also involve transitioning farmland in the Great Barrier Reef catchment from sugar cane plantations, which use fertilisers that cause much of the water pollution in the reef, to a less high-intensity form of agriculture, such as grazing.

“There’s things that could be done for the water quality part but it’s hard to see this government doing them,” Brodie told Guardian Australia. “The federal government is unfortunately just writing the Great Barrier Reef off. Other things are more important to them, like the support of farmers in Queensland, and the coal industry.”

Brodie said improving water quality would “not be enough by itself” to save the reef, which faces its most direct threat from climate change.

But unlike climate change, Brodie said, the quality of water flowing into the reef is directly under the control of existing Australian legislation. Improving water quality cannot prevent future bleaching events, but it can improve the capacity of the reef to recover.

The environment minister, Josh Frydenberg, welcomed the Unesco draft decision on Saturday, which he said “confirms the Reef 2050 plan has been effective”.

“The draft decision points to the importance of the reef’s resilience despite the challenges faced from coral bleaching,” he said.

Frydenberg acknowledged the committee’s push for accelerated action on water quality and said international efforts to reduce greenhouse gas emissions was “critical for reefs worldwide, including the Great Barrier Reef”. He cited Australia’s continued commitment to the Paris agreement, which the US president, Donald Trump, abandoned on Friday, as evidence of Australia’s efforts.

Unesco is expected to release a second report on the impact of climate change on the health of all world heritage listed reefs before the July meeting.

Richard Leck, oceans campaigner for the World Wildlife Fund, said that while the impacts of water quality and land clearing on the health of the reef were significant, climate change remained the major threat.

If the global climate warmed by 1.5 degrees, Leck said, the Great Barrier Reef would not survive. “We need to have climate policies that will actually protect the reef and currently our climate policies are nowhere near sufficient to get the action required to save the reef,” he said.

The Australian Marine Conservation Society seconded that concern, and called on the Queensland government to immediately introduce land clearing laws, scrapped under the Newman government, to reduce the amount of runoff flowing into the reef’s catchment.

The Palaszczuk government tried to reintroduce land-clearing laws in 2016 but failed to get them past parliament.