29/03/2016 11:07 AM AEDT | Updated 15/07/2016 12:51 PM AEST

Coral Bleaching Is Highlighted In Tropical Footage From The Air

This stunning footage of a helicopter ride over the Great Barrier Reef sets off major reds flags for scientists.

To the untrained eye, it's an idyllic coastal scene, but researchers looking for signs of coral bleaching see absolute devastation of one of Australia's most diverse ecosystems.

National Coral Bleaching Taskforce convener Terry Hughes said researchers couldn't help but feel emotional.

“This has been the saddest research trip of my life,” Hughes said in a statement.

White shapes in the shallows show patches of bleached coral.

“Almost without exception, every reef we flew across showed consistently high levels of bleaching, from the reef slope right up onto the top of the reef.

"We flew for 4000km in the most pristine parts of the Great Barrier Reef and saw only four reefs that had no bleaching."

Researchers covered reefs from Cairns to Papua New Guinea.

Coral bleaching can be caused by hotter sea temperatures that can cause the colourful photosynthetic algae inside coral to be expelled.

Without the algae, the coral is white -- bleached -- and if temperatures drop quickly, the algae can recolonise them, but if it stays hot too long, the coral dies, leaving a bleached white shell.