Scuba Divers May Be Damaging Coral Reefs Far More Often Than They Realize Due to Underwater Dunning-Kruger Effect

A new study finds that even environmentally conscious divers smash, scrape, and stir up reefs. The biggest culprit? Their own overconfidence.

If you’ve ever strapped on a tank and slipped beneath the waves to glide past a coral garden, you probably considered yourself to be one of the good ones. Scuba divers, after all, tend to love the ocean. They pay good money to see it. Many fill out surveys swearing they’d never harm a reef.

The reef tells a different story.

A new study from the University of Sydney, published in Conservation Letters, watched more than 700 scuba divers at popular tourism sites in the Philippines and Indonesia — including Bali — and tallied every time fin, hand, knee, or dangling gauge touched coral. Over 300 hours of underwater observation, researchers recorded 4,981 reef contact events among 411 divers. Approximately 41% of those contacts caused visible damage, ranging from snapped coral branches to clouds of stirred sediment that choke the reef’s filter-feeding tenants.

The average diver made contact with the reef roughly once every four minutes and spent nearly two seconds of every minute physically touching it. While it doesn’t sound like much, multiply that across the heavily trafficked dive sites of Southeast Asia, and a picture emerges that the dive industry doesn’t love to advertise.

“This work documents the unsustainable underwater footprint of scuba diving tourism on coral reefs,” said lead author Bing Lin, who began the project as a PhD student at Princeton and finished it at Sydney’s Thriving Oceans Research Hub.

The unknowing damage

Here’s the unsettling part: More than 80% of the harmful contacts were unintentional or simply went unnoticed by the diver doing the damage. These weren’t reckless tourists ripping souvenirs off a reef. Most divers in the study self-reported strong pro-environmental attitudes. They cared. They just didn’t notice their fins back-kicking into a stand of staghorn.

Researchers found it concerning when they compared what divers thought they were doing with the damage they were actually doing. Divers underestimated how often they touched the reef by nearly fivefold.

“Many divers believe they are careful and low impact, but our data shows a consistent mismatch between perception and behavior,” Lin said.

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The psychology is where the study gets more interesting — and where most of us, diver or not, might wince a little in recognition.

According to the study, three-quarters of divers rated themselves as “above average” at avoiding reef contact compared to their peers. This is a textbook case of “illusory superiority” — the same bias that, in Ola Svenson’s classic 1981 study, “Are we all less risky and more skillful than our fellow diver?”, led the vast majority of drivers to rate themselves safer and more skillful than the median person behind the wheel.

The researchers also documented the infamous Dunning-Kruger effect underwater: the least skilled divers tended to overestimate their abilities the most. The people doing the most damage were often the most convinced they were doing none.

The camera and the octopus

A few specific factors reliably cranked up the harm. Divers carrying underwater cameras, wearing gloves, or holding pointer sticks made more contact with the reef — likely because the gear changes how divers move, what they pay attention to, and how close they’re willing to get for “the shot.”

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Peer pressure mattered too. When one diver in a group touched the reef, others became much more likely to follow. Reef-touching, it turns out, is socially contagious.

However, the single most significant amplifier was the very thing tourists pay to see: wildlife. When a turtle, shark, or reef fish appeared, intentional reef contacts jumped 220%, unintentional contacts rose 85%, and damaging contacts went up 106%. Divers, hypnotized by a passing creature, drifted closer than they meant to and braced themselves on whatever happened to be there.

The study also found that a small minority of divers were responsible for a disproportionate share of the damage, which, depressing as that sounds, is actually encouraging news. It means well-targeted interventions could go a long way.

A small footprint with a long shadow

Coral reefs are already taking punches from every direction: ocean warming, marine heatwaves, acidification, pollution, overfishing. Set against mass bleaching events that have killed corals across vast stretches of reef worldwide, a diver bumping a reef with a fin can feel almost trivial.

But Lin’s earlier research, published in Nature Sustainability, showed that coastal tourism, including scuba diving, leaves a regionally detectable mark on reefs across entire archipelagos. The bumps add up. And they layer on top of every other stressor that a reef is already trying to survive.

The fix isn’t to ban diving. Tourism keeps reef economies afloat in many of the world’s most biodiverse coastal regions, and divers are often some of conservation’s most passionate advocates. The researchers point to better buoyancy training, tighter rules on cameras and gear, stronger environmental briefings, and higher certification standards for both divers and operators.

The deeper hurdle is psychological. You can only ask people to fix a problem they believe they’re part of.

“First and foremost, divers need to understand that they are a part of the problem before we can convince them to become a part of the solution,” Lin said.

The fix begins with a humbling thought: The most dangerous diver may not be the careless one. It may be the careful one who is sure they already know what they are doing.