This is the disparity that explains why Pauline Hanson chose to snorkel where she did last week, while giving the Great Barrier Reef a clean bill of health.
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New data released late on Monday shows that in the south - including around Great Keppel Island, where One Nation Senators took to the water - 99 per cent of coral survived the bleaching event last summer.
Head further north, to the 700-kilometre stretch of shallow-water reefs north of Port Douglas, and it is estimated 67 per cent of coral in this area has died since February.
Terry Hughes, director of the ARC Centre of Excellence for Coral Reef Studies, said recent underwater surveys had confirmed that bleaching due to increased ocean temperatures in February and March was the worst on record, but that the rate of death had varied markedly.
"The bleaching has turned the barrier reef into a giant jigsaw puzzle," Professor Hughes said.
"Areas in the south that were mildly bleached earlier in the year have recovered. Areas in the north that suffered worse bleaching have had catastrophic mortality."
The area between Port Douglas and Cape Melville, taking in reefs around the research station on Lizard Island, is in the worst shape. Depending on the reef, it is estimated between 47 and 83 per cent of coral is dead.
Head further north and the extent of the damage depends how close you are to the shore. Shallow, coastal reefs up past Cape York to Papua New Guinea are as badly affected as the Lizard Island region.
But reefs further out, near the eastern edge of the continental shelf, suffered a smaller rate of coral loss. About a quarter of the coral was found to have died – probably due to cooler waters welling up from the Coral Sea.
Down south, it is a much happier story. It is estimated just 6 per cent of coral cover died in the region where most tourists go, between Port Douglas and Mackay. The mortality south of Mackay was only 1 per cent. Scientists believe the tail-end of Cyclone Winston rapidly cooled waters here in February, as the north was feeling the combined effects of global warming and an El Nino event in the Pacific.
It was here that One Nation visited on Friday, prompting Senator Hanson to declare "people with their own agendas" were telling lies about the health of the reef and wrecking the tourism industry.
The Great Barrier Reef Marine Park Authority said on Monday it was seeking further information about coral collected from a reef and brought to the surface to show the media during the One Nation snorkel trip.
In an emailed statement, the authority said it understood a member of the Senators' party had a research permit, but it was reviewing the situation. Touching and collecting coral is illegal in the marine park without a permit.
The data released on Monday is backed by the marine park authority and the Australian Institute of Marine Science, both government bodies.
It follows the marine park authority earlier this year estimating 22 per cent of coral along the reef died during the bleaching.
When the water is warmer than 30 degrees, corals expel the zooxanthellae marine algae that give them energy and colour. If the water stays that warm for more than eight weeks the coral starts to die.
This is the third major bleaching event on the Great Barrier Reef, following damaging seasons in 1998 and 2002. Professor Hughes said the death rate in the worst hit areas this year may yet increase due to predation by Drupella, a type of sea snail, and crown-of-thorns starfish.
It is expected the northern region will take 10-to-15 years to regain the lost coral, if it is allowed time to recover.
Professor Hughes has estimated the next major bleaching event is most likely in five years during the next El Nino, but could be sooner or later, and that bleaching events could be annual by 2030 if the current greenhouse gas emissions trajectory continues.
