Hywel Williams has urged a halt to diving

Three other divers have died at the site in the last four months.

Hywel Williams, the Plaid Cymru MP for Caernarfon, has renewed his plea for divers to stay away from the quarry until safety measures are in place.

"I recognise people's rights to take risks as long as those risks are well- thought through and there are adequate safety measures," said Mr Williams.

"I think the danger here is people may be venturing beyond their capacities without quite realising what they are doing."

Police and ambulance crews attended the scene at 1340 GMT on Saturday when Mr Amison was reported to be in trouble in the pool, which is 108m at its deepest point.

North Wales Police were unable to say on Sunday whether Mr Amison had been diving alone or as part of a group.

It was also unclear if he had been free-diving or had been using aqualungs.

The quarry is popular with diving enthusiasts

In December 2001, Mick Gott from Derbyshire and Jason Barrass from Preston died in separate accidents at the Dorothea quarry within 48 hours of each other.

Another diver had died at the site in the previous month.

Mr Williams - who spoke out last year against the risks divers were taking - renewed his call for safety measures following the latest tragedy.

He supported plans for permanent diving facilities at the site and checks to make sure divers knew what they were doing.

"That's one of the ways to get at this problem - to make sure the divers who use the Dorothea ...are up to the mark," he said.

Local councillor Les Jones said the owners of the quarry ought to do more to block access to the site.

Les Jones says the owners should do more

He said: "They should at least make an effort to stop people from coming to the quarry to dive and to stop these tragedies taking place."

However, the quarry owners have regularly warned divers that they are trespassing.

Attempts have also been made to block access to the pool with little success.

The owners have urged divers to stay away until they have developed a formal diving centre and first aid facilities.

Diving experts say the quarry is steep-sided and gets very cold, which can lead to accidents including breathing equipment freezing up.

Despite the latest tragedy, enthusiasts were continuing to dive at the lake on Sunday.

The flooded quarry is one of the deepest fresh water sites in Europe and is a popular attraction for scuba divers.