A married father-of-two died while taking a dive course run by a school at which standards were "casual" or "slap-happy", an inquest has heard.
Mr Pye's body was found five years after he died in the sea off Portland
Roger Pye, 51, from Walton-on-Thames, Surrey, was taking part in a deep dive off Portland, in Dorset in 2001.
Aquasplash owner Nigel Band was his buddy but left him to help a female student whose belt had slipped off.
The coroner recorded an open verdict in the case of Mr Pye, whose body was found five years later on the sea bed.
The inquest in Dorchester heard how the management consultant had suffered problems during the dive, on 30 September 2001.
After his buddy left him he was seen floating high in the water before sinking.
Coroner Michael Johnston said: "I can't say any specific action or inaction of Nigel Band contributed to his death.
"I think his actions might have created an environment where an incident could happen that led to Roger's death.
"[The Health and Safety Executive] was given the impression that Mr Band's training was casual or perhaps slap-happy."
Judith Tetlow, HSE principal inspector and dive specialist, told the inquest an investigation found "a number of things that caused concern".
She said students were not given enough air and had to rely on their buddy's supply and legal forms and medical declarations were not completed before the dives.
The HSE prosecuted Mr Band under the Health and Safety at Work Act but he was acquitted of any wrong-doing.
He has since moved abroad and did not attend the inquest and Aquasplash is no longer trading.
Mr Pye's body was found on 28 April, 2006, by a diver out spear fishing.
He was identified using DNA and from a bank card in his trouser pocket.