Divers have captured concerning footage of what conservationists believe to be widespread coral bleaching at Western Australia's Ningaloo Reef.
Photographs and video footage of the world heritage-listed reef have since been published online, leading authorities to demand a strong response from the government.
Australian Marine Conservation Society WA Director Paul Gamblin described the images as "heartbreaking".
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There have been calls from the environmental group over the past two months, warning of the impacts caused by a marine heatwave.
The group said the heatwave threatens the world-renowned Ningaloo Reef ecosystem.
"To see beautiful coral reefs bleaching white at Ningaloo icons, including Turquoise Bay, Coral Bay and Bundegi, is just devastating," Gamblin said.
"Bleaching at Ningaloo is not normal. It demands urgent action from government, not business as usual. Large areas of coral could die in the weeks ahead. This is a red-alert moment for Ningaloo.
"This marine heatwave is like an underwater bushfire raging along Western Australia's coast killing tens of thousands of fish that washed up on Pilbara beaches and now it's cooking Ningaloo, the jewel in the crown."
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The environmental group has called for greater transparency and regular updates from state and federal ministers about the developing marine heatwave.
Last month, more than 30,000 fish washed up dead on Gnoorea Beach, south of the Ningaloo Reef.
"We called for the WA government to address this destructive marine heatwave weeks ago after the fish kill, and there has been silence at the ministerial level," Gamblin said.
"Surely now that there is such widespread bleaching at Ningaloo, someone in government will step up.
"We know that many people in Exmouth are distressed by what they are witnessing, and they need and deserve a clear response from government.
"It's also a stark reminder that coastal communities and their businesses, including the fishing industry and Ningaloo's world-renowned tourism industry, rely on a healthy marine environment, and climate change poses an existential threat to them."
Gamblin called on each government to "reduce pressure on (the) stressed marine environment".
"In addition to Ningaloo, we also need to urgently know the status of bleaching at WA's spectacular offshore coral reefs, including Scott Reef and the Rowley Shoals," he said.
"It's time we listened to our scientists who have been warning for decades that climate change would threaten Ningaloo as it already has the Great Barrier Reef and many other coral reefs around the world.
"WA's spectacular coast, so core to our identity and economy, is clearly not immune to the destructive impacts of climate change."
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