The worst "mass" die-off of coral in the Great Barrier Reef was recorded this year, with the "most-pristine" parts of the reef being hit the most.

More than 435 miles in the north of the 1,400-mile-long reef were stripped of 67% of the shallow-water coral. It was noted that historically, the northern section of the reef had been least affected by human activity. The bleaching was due to warming waters, according to nytimes. In the southern portion of the reef, a cyclone that brought down temperatures saved the cyclone too.

"Most of the losses in 2016 have occurred in the northern, most-pristine part of the Great Barrier Reef," said Prof Terry Hughes, the director of the ARC Center of Excellence for Coral Reef Studies at James Cook University in Townsville, in the eastern state of Queensland. "This region escaped with minor damage in two earlier bleaching events in 1998 and 2002, but this time around it has been badly affected."

This is the third and worst coral bleaching event in this region for the past 18 years. In 2002, the reef's coral been found to have increased by 19%, said the Australian government.

"To see those sections, two-thirds of the northern section, dead, is catastrophic," explained an Australian environmental minister. 

Experts explain that it would take 10 to 15 years to regain the coral lost due to bleaching event, but only if there isn't a fourth event.

There is one phenomenal quality of the GBR that has been lost forever. Even if it goes back to its pre-bleaching levels, it can never get back the diversity that it once had.

Measures to save and restore the Reef are on. While the UN is considering adding the Great Barrier Reef to the list of threatened world heritage sites, the Australian government is planning to spend $1.5 billion to protect it in the next decade.