Paul Kay believes the death toll could have been higher
On Saturday the infamous Dorothea quarry claimed the life of its 21st victim.
The quarry lake in Gwynedd, north Wales, is up to 300ft deep in places with a network of flooded tunnels and sheer drops.
Despite its danger it is a favourite training location for amateur divers from across the UK, who go there unofficially because it is private property.
On Saturday 31-year-old Jason Dean from the Wirral, failed to resurface during a group dive.
Twenty other divers have drowned in the pool in the Nantlle Valley in the last 10 years - six in the past year.
There had been plans to set up a diving school at the quarry, but it is now for sale for more than £1m.
Here Paul Kay, an underwater photographer with over 20 years diving experience, explain to News Online why the site is so deadly and what it is about the sport that carries such high risks.
"I don't think there is anything fundamentally dangerous about Dorothea itself - the trouble is that it is unregulated and people think they can do things they can't.
"I have heard some horror stories about people pushing themselves too far who are then just unable to recover.
"I've talked to divers who've confirmed some are diving on air down to 100 metres when the accepted limit is 50 metres - it's absolutely lunacy.
"It does attract a element who see sub-aqua diving as a macho thing but the paradox is that petite women, because of their breathing, make very good divers - so these people are kidding nobody.
"The death toll at the quarry could be an awful lot higher as there have been an awful lot of near misses and lucky escapes.
"I don't think anyone has died there because they've got a death wish. It's just they've got into difficulties.
Mr Kay believes a regulated centre would 'kick out' those taking risks
"All the stories are about divers who are fully trained or with quite a bit of training who are pushing themselves and getting into difficulty.
"The cold and the depth are the two things you have to deal with - it's terribly cold in the winter.
"Quite a few people have drowned and some have had heart attacks.
"Diving can sometimes be very stressful - I think the problems at Dorothea can cascade out of control.
"Diving is a relatively safe adventure sport...if you look at the statistics of accidents, it is quite low down.
"Although the Dorothea site has to some extent given sub-aqua diving a bad name, if it was properly regulated it could be a premier centre but it would take a lot of investment."