Keen to explore the murky depths, the duo ascended into the cold water.
A little over 30 feet beneath the surface is a sandstone ledge, and on that ledge the two divers found the mutilated body of New Zealander Marty Johnstone.
The discovery would not just lead to a murder trial, it would throw open the doors on an international drug-smuggling operation.
This is the story of the handless corpse.
Chinese symbol inscribed on a bluestone medallion around the Delph Quarry corpse's neck meant "long life". It was a strange clue for Lancashire Constabulary officers: one that simultaneously told them a lot about the individual they had pulled from the cold water, while muddying the case in more confusion and mystery.
The long life symbol inspired papers to dub the discovery of the mutilated corpse as a "Chinese Puzzle". The body was naked and anchored beneath the water with industrial weights and a hydraulic lorry jack.
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Reading and Ashcroft were members of the Newton-le-Willows sub-aqua club.
"At first we thought it was a tailor's dummy," 22-year-old Ashcroft told the Liverpool Echo.
"It was only when we got close, we found it was a body and had no hands, our stomachs turned."
Though the body was not identified immediately, police knew this was a lot more than just evidence of a murder and it was widely reported that the killing was a "gangland-style" execution.
The victim, a powerfully built male, who could have been aged between 25 and 35, had severe stomach and head wounds, and was handless, preventing any fingerprint identification.
He was 1.88m tall, suntanned, had good teeth, a neatly trimmed moustache, and shoulder-length brown hair. Not the typical look of a man from Lancashire. Three cars were also pulled from the quarry and forensically checked but police were keen to tell the public it was commonplace for stolen cars to make their way to the bottom of the quarry.
In fact, when it was drained in 1999, hundreds of cars were found beneath the water.
Soon after the body was discovered police launched a murder inquiry involving more than 80 officers.
Police spokesman Ray Rimmer said: "We can't say at this stage what caused the wounds to his head and stomach but either could have been sufficient cause of death."
That mystery was soon solved.
On Tuesday, October 16, it was revealed the man had been shot in the head. Officers believed the shot had been fired from close range, probably using a revolver.
According to pathologists the man also had several knife wounds to the stomach and his hands had been hacked off after death.
Police were eager to follow the trail of the strange medallion, sure that it would lead to the feet of the killer.
Rimmer, leading the investigation, could not rule out the possibility the medallion had been placed around the victim's neck as some sort of macabre joke by his killers.
Police began to follow the trail of the Chinese symbol and visited several specialist shops in Liverpool to try to source it. This yielded few results.
A team of officers visited Walton Gaol in Liverpool, hoping gangland killers or criminals could shed a light on the victim, but the criminal underworld was not willing to play ball.
By October 26, two weeks after the body was discovered, several questions still remained: Who was the victim? Why was he killed? Where did the murder take place?
One thing was certain, he was not meant to be found at all. His clothes were gone, and his hands; his mouth was a mess where someone had attempted to smash out his teeth. Any identifying marks had been stripped away making it more and more likely that the medallion did not belong to the victim but had been placed about his neck.
y the end of October every police force in Great Britain and Northern Ireland was circulating images of the man found in Delph Quarry.
The stretch of idyllic Lancashire countryside had become known across the country for the grisly discovery and police were fast running out of ideas when it came to finding the killer or identifying the body.
On October 26 Rimmer told the media he was surprised no one had recognised the victim's distinctive looks and suggested he might have changed his appearance to avoid detection.
What they didn't know then was that the man fished out of the quarry was caught up in a complex and far-reaching drug trade.
Terry Clark, known by several aliases - Terry Sinclair, Alexander James Sinclair, Tony Bennetti, the Australian Jackal and Mr Big - was a New Zealander who ran a violent and prolific heroin trade involving Britain, Australia and his native New Zealand. But he didn't run the operation, based in Singapore, alone.
The other man running the operation alongside Clark, had been given the name "Mr Asia" in several newspaper articles about his exploits in Auckland. He was Christopher Martin "Marty" Johnstone.
Back in England, police had a breakthrough on November 2, almost three weeks after the body was discovered, when former beauty queen Julie Hue and her friend Barbara Pilkington walked into Leyland police station in early November and told police who the dead man was.
The man was 27-year-old Marty Johnstone from New Zealand, Hue's boyfriend.
She had been on holiday in Spain with Pilkington when Johnstone was murdered. She was told he was on business in New York and couldn't be contacted, but had grown suspicious and then alarmed when he failed to call her on her 22nd birthday.
Hue also told police that her boyfriend had met his fate at the hands of one Andrew Maher from Leyland, the common-law husband of her friend Pilkington.
Police told the Mirror they were 99.9 per cent certain the body was Johnstone, and described him as a "New Zealand businessman dealing in drugs".
Already they were forming theories about a power struggle going wrong and reported they had held 28 people from across Lancashire under suspicion of murdering Johnstone.
Australian officials were on their way to Chorley, keen to establish whether the so-called "Kiwi link" existed.
By November 5 the case had been blown wide open. Days after Johnstone was identified, armed police were used to protect five men who appeared briefly in Chorley Magistrates Court to answer charges of killing Johnstone.
James Smith, 27, of Livingstone Scotland, Frederick Charles Russell 38 of London and Keith William Kirby of Clayton Brook, Lancs were the less significant figures standing trial for murder. The names that stood out were Andrew Samuel Maher, a 26-year-old from Leyland and a New Zealander, based in London, called Alexander James Sinclair.
The case would become the most expensive and heavily guarded in British history.
On November 8, police searching a river in Scotland found a severed right hand. A pathologist later linked it to Johnstone allowing the police to formally identify their victim and slot together a crucial part of the story.
Clark and Johnstone had first become acquainted in the 1970s when Clark was already a multimillionaire drug-runner.
Johnstone moved from New Zealand to Australia where he teamed up with Clark and also met Maher. The trio formed a syndicate, smuggling drugs from Thailand into Australasia.
At its height, the operation saw vast amounts of cocaine and cannabis transported by boat across the world while the three men set up companies in Australia, Hong Kong and Singapore.
Clark was not a soft touch. He routinely murdered those who blabbed to the police in Australia.
Mounting police inquiries after the discovery of two bodies in a shallow grave in Australia, forced Clark and Maher to leave for England, avoiding the authorities - and working on the premise that exporting drugs to Britain could also be lucrative.
With the move, and the distance between them, Clark started to cut Johnstone out of the deals.
He also switched from dealing in cannabis to heroin, transporting drugs by plane and leaving Johnstone in his wake when it came to the modern trade.
Johnstone and Maher, in contrast, were close friends; Maher naming his daughter Marti after his best mate. But the two would soon be ripped apart.
In 1979, Johnstone flew to London to visit Clark who gave him $50,000 to find a new source of heroin. On August 1 that year, Johnstone went to Pattaya, Thailand, eager to complete a heroin deal. But he was tricked by the Thais who took $35,000 for one bag of heroin.
Knowing Clark would be happy to cut his throat for such an indiscretion, Johnstone panicked and mixed the 700-gram sample bag he had bought with caster sugar while in Bangkok.
At this point Clark had lost patience with "Mr Asia".
Johnstone was flashy, keen to splash his cash but had done very little of the dirty work and now was haemorrhaging money from the organisation for little gain.
Clark and Johnstone were also cocaine addicts and paranoid to boot. They didn't trust each other and their organisation was buckling under the weight of multiple murders, backstabbing, bust deals and now this.
Mr Asia and Mr Big were soon to go from a duo to a single entity and Clark was keen to bump off his partner now rather than later.
Maher, still only 26, was tasked with carrying out the killings. Fearing for the safety of his wife and daughter, he agreed.
Other associates were roped in to source a weapon and to help cover their tracks.
Russell, from London, supplied the gun. It had been brought to London in a shoebox by 16-year-old Karen Pidgeon, the daughter of one of Clark's chauffeurs. Kirby, of Clayton Brook, was one of Maher's friends from school and supplied the weights and rope used to bury the body underwater. The plan was simple.
Meanwhile, a paranoid and scared Johnstone, with a bag of caster sugar and $15,000 of Clark's money, would be put in touch with a Glasgow contact who could supply him. Scotland would become Britain's heroin capital in the 1980s, so a deal there made sense.
Johnstone arrived in England, and on October 9 he and Maher set off for Glasgow. They drove up the A6 on the pretence of driving into Scotland and securing a drugs deal.
At some point, perhaps near Carnforth, north of Lancaster (the location is still not exact), Maher stopped the car, before shooting Johnstone in the head at point-blank range.
He and Smith took the body back to Maher's garage in Robin Hey, Leyland.
Keen to remain undetected, the two men set about butchering the body, using an axe to slice off Johnstone's hands before taking a lump hammer to smash out his teeth. However they were unable to deal much damage to Johnstone's gnashers.
They slashed open his stomach to ensure that he didn't float and tied the weights, supplied by Kirby, to the body. The corpse was roughly folded into Maher's Jaguar and taken to the quarry, where it was pushed in.
he five men appeared in Chorley Magistrates Court again on May 19, 1980, but the formal trial didn't begin until January 1981.
One hundred witnesses were to be called and the Crown Court at Lancaster Castle was heavily guarded by police. The Liverpool Echo described it as a "siege fortress" with more than £100,000 of security organised for the proceedings.
Eight days into the trial Maher admitted that he was given a 'kill or be killed' ultimatum by Clark before he shot Johnstone. He would later plead guilty to the charges.
In April, Clark told the court that he was "no lily-white angel" but was not guilty of the crime. Unfortunately, by this point, prosecutors in Britain and Australasia were sure that he was Mr Big and continued to try to prove that to the jurors.
On July 15, 1981, 123 days after the trial began, Clark was convicted of murder and sentenced to life imprisonment with a 20-year recommendation. The same sentence was handed out to Maher, while Smith, Kirby and Russell all received life sentences for their part. In his closing notes the judge called Clark "ruthless and dangerous".
But within two years he was ruthless, dangerous and dead - having suffered a heart attack in prison in 1983.
Maher must have behaved badly because he served more than 20 years behind bars and died there in 2011.