The first survey for 2017 was conducted on Thursday by the Great Barrier Reef Marine Park Authority (GBRMPA), over the area between Cairns and Townsville in northern Queensland. Climate change is compounding the reef's woes as warming waters put corals in a precarious position to survive.
The Great Barrier Reef is the world's largest collection of coral reefs, with 400 types of coral, 1,500 species of fish and 4,000 mollusc species, and is the habitat of wildlife such as the dugong - sea cow - and the large green turtle. The full extent of the bleaching will take weeks to tease out as the reef covers an area roughly the size of Germany.
He said not all bleached coral would die, and a year ago revealed bleaching and mortality could be highly variable across the vast marine park, a World Heritage Site which covers an area larger than Italy. Waters in the region have rapidly warmed over the past two months and are now up to 5.4°F above normal.
Dr Neal Cantin, from the Australian Institute of Marine Science (AIMS), said the recurrence of widespread coral bleaching in back-to-back summers indicated there was not enough time since 2016's extreme heat event for the corals to fully recover.
Australia's Great Barrier Reef has been shown to have an even worsening coral bleaching situation on Friday, with Greenpeace releasing photos and footage of the damage they say is caused by climate change.
Images released by Greenpeace add to what the US National Oceanic and Atmospheric Administration has described as reports of "scattered coral bleaching along a large stretch" of the reef.
"As we saw past year bleaching and mortality can be highly variable across the 344,000 square kilometre Marine Park - an area bigger than Italy", he said. The heat causes them to die off or be expelled, leaving behind ghostly white coral skeletons.
"Mass bleaching is occurring on the Great Barrier Reef for the second consecutive year". For scientists who have studied the reef for years, that development brought them to tears because it foretold what the future holds for the reef unless carbon pollution is cut.More news: Aston Martin Launches New Brand AMR At 2017 Geneva Motor Show
The coral may die in the six to 12 months after bleaching, meaning the level of mortality on the reef will not be determined until later in the year.
The iconic status of the Great Barrier Reef gives it the most attention in coral bleaching.
Bleaching warnings and alerts over the past 90 days. The corals aren't getting the chance to bounce back from last year's bleaching event.
As per World Heritage Convention guidelines, Australia had a "primary responsibility for protecting and conserving the Great Barrier Reef" and it "must address both existing and potential threats to the reef, whatever their source".
Losing one of the most awesome features on the planet is in and of itself a disturbing prospect, but it's also a dollars and cents issue.
Corals can recover if the water temperature drops and the algae are able to recolonise them.
"What we know so far is the reef is showing further signs of bleaching", Mr Miles said.