Global Warming (coral reefs / dive-zone reopening)
A year ago, in May 2024, these zones were declared closed to tourist visits after specialists identified a problem: the reefs had begun bleaching en masse due to environmental stress caused by rising water temperatures. From the heat, the corals lost their symbiotic algae (zooxanthellae), which left them brittle and unable to survive. As a result, the entire Phi Phi archipelago, along with several neighboring islands, had to be temporarily cordoned off. Ten popular diving zones stayed closed to eager tourists for nearly a year.
But what do tourists have to do with it, if the main damage to corals comes from global warming? Are people's own bodies really raising the water temperature enough to disrupt the underwater microclimate? Of course not! Let's break down exactly how humans threaten a bleached, and therefore weakened, coral reef.
Tourists add extra stress to corals
Even though the main danger is rising water temperature, corals become even more vulnerable when local stressors pile on top of that:
Physical damage: touching, stepping, anchors, fins. When everything around you is this beautiful, it's easy to lose track of your own size. A diver's fin can accidentally brush a coral branch and snap it off — and corals grow painfully slowly, just 1 to 3 cm a year. On top of that, every diver stirs up clouds of sand from the seabed while swimming, and that sand settles on the branches and makes it harder for them to "breathe."
Cloudy water: tourists feed bread to fish, and motorboats pollute the water with petroleum products. Boats mooring near islands almost always drop anchor blindly, damaging corals without anyone even noticing.
Pollution: sunscreen, food waste, and other litter left behind, one way or another, after waves of tourists pass through. Sunscreen? Yes. It contains compounds like oxybenzone and octinoxate, both of which harm the development of young coral polyps and can even cause mutations in their DNA. Sunscreen also contains zinc and titanium, even if only in trace nano-amounts, which can affect zooxanthellae at the molecular level. And of course, sunscreen leaves a film on the water's surface that makes it harder for photosynthesis to happen in the depths below.
It's clear now just how risky even a slow-paced activity like diving can be for a coral reef ecosystem. And snorkeling is hardly any gentler!
In short, corals already weakened by high temperatures lose their symbiotic algae from almost any additional outside pressure — which means that, alongside time to heal, they also need rest. Imagine getting a burn, and then a scratch on top of that burn. Sounds awful, because to survive a scratch, the burn needs to have healed over with a fresh layer of skin first! The same logic applies here: time heals.
Time heals
Over the course of the year, the water grew cleaner, the corals got more light and oxygen, zooxanthellae began returning, new polyps started taking hold, and the reefs began recovering faster.
With that in mind, on April 17, 2025, the authorities of Hat Nopparat Thara–Mu Ko Phi Phi National Park announced the reopening of 10 zones for snorkeling and diving:
Conclusion
But recovery hasn't been satisfactory everywhere. The western side of Koh Kai (Ao Khang Khao) remains closed to protect especially sensitive stretches of reef.
Park authorities are urging all tourists, guides, boat operators, and captains to strictly follow the rules: no littering, no dumping food waste into the sea, no anchoring on reefs, and no touching or stepping on corals or marine life.
These measures are meant to protect the marine ecosystem and support the reefs' continued recovery.
A year ago, in May 2024, these zones were declared closed to tourist visits after specialists identified a problem: the reefs had begun bleaching en masse due to environmental stress caused by rising water temperatures. From the heat, the corals lost their symbiotic algae (zooxanthellae), which left them brittle and unable to survive. As a result, the entire Phi Phi archipelago, along with several neighboring islands, had to be temporarily cordoned off. Ten popular diving zones stayed closed to eager tourists for nearly a year.
But what do tourists have to do with it, if the main damage to corals comes from global warming? Are people's own bodies really raising the water temperature enough to disrupt the underwater microclimate? Of course not! Let's break down exactly how humans threaten a bleached, and therefore weakened, coral reef.
Tourists add extra stress to corals
Even though the main danger is rising water temperature, corals become even more vulnerable when local stressors pile on top of that:
Physical damage: touching, stepping, anchors, fins. When everything around you is this beautiful, it's easy to lose track of your own size. A diver's fin can accidentally brush a coral branch and snap it off — and corals grow painfully slowly, just 1 to 3 cm a year. On top of that, every diver stirs up clouds of sand from the seabed while swimming, and that sand settles on the branches and makes it harder for them to "breathe."
Cloudy water: tourists feed bread to fish, and motorboats pollute the water with petroleum products. Boats mooring near islands almost always drop anchor blindly, damaging corals without anyone even noticing.
Pollution: sunscreen, food waste, and other litter left behind, one way or another, after waves of tourists pass through. Sunscreen? Yes. It contains compounds like oxybenzone and octinoxate, both of which harm the development of young coral polyps and can even cause mutations in their DNA. Sunscreen also contains zinc and titanium, even if only in trace nano-amounts, which can affect zooxanthellae at the molecular level. And of course, sunscreen leaves a film on the water's surface that makes it harder for photosynthesis to happen in the depths below.
It's clear now just how risky even a slow-paced activity like diving can be for a coral reef ecosystem. And snorkeling is hardly any gentler!
In short, corals already weakened by high temperatures lose their symbiotic algae from almost any additional outside pressure — which means that, alongside time to heal, they also need rest. Imagine getting a burn, and then a scratch on top of that burn. Sounds awful, because to survive a scratch, the burn needs to have healed over with a fresh layer of skin first! The same logic applies here: time heals.
Time heals
Over the course of the year, the water grew cleaner, the corals got more light and oxygen, zooxanthellae began returning, new polyps started taking hold, and the reefs began recovering faster.
With that in mind, on April 17, 2025, the authorities of Hat Nopparat Thara–Mu Ko Phi Phi National Park announced the reopening of 10 zones for snorkeling and diving:
- Koh Kai (Chicken Island), north side
- Koh Kai, east side
- Koh Poda, north side
- Ao Pu Ya Bay, Koh Poda
- Koh Daeng
- Railay Bay
- Koh Yawasam
- Loh Ba Kao Bay
- Viking Cave
- The front section of Pileh Bay
Conclusion
But recovery hasn't been satisfactory everywhere. The western side of Koh Kai (Ao Khang Khao) remains closed to protect especially sensitive stretches of reef.
Park authorities are urging all tourists, guides, boat operators, and captains to strictly follow the rules: no littering, no dumping food waste into the sea, no anchoring on reefs, and no touching or stepping on corals or marine life.
These measures are meant to protect the marine ecosystem and support the reefs' continued recovery.
Ten diving and snorkelling spots in Krabi Province reopened to tourists on April 17.
Diving Is Back On!
Original text translated by Claude