Dale Pike, 25, of Glynneath, Neath Port Talbot, "stood and watched" as Gareth Pugh dived into the lake with a weighted belt to fish out balls.
Mr Pugh's body was found in the water at Peterstone Lakes Golf Club, near Newport, after he lost his breathing equipment and drowned in February 2016.
Pike received 32 months after admitting manslaughter by gross negligence.
Cardiff Crown Court heard Pike raised the alarm when he noticed a constant stream of bubbles rising to the lake's surface and a flotation device carrying Mr Pugh's air supply floating towards the edge.
Emergency service staff pulled him from the water 70 minutes after he first entered and he was found with his feet pointing upwards, weighed down by a weighted belt and a 16kg (35lbs) bag of 341 golf balls he had retrieved.
The court heard Pike, who ran Boss Golf Balls which sells balls retrieved from lakes, should have hired trained divers to carry out the work, at a cost of about £1,000 a day.
But instead he employed Mr Pugh, who had ADHD and learning difficulties, and paid him £20-40 a day.
David Elias QC, defending, said Pike "naively and foolishly believed that all would be well with the use of that equipment in that lake".
Sentencing Pike, Judge Keith Thomas said: "Mr Pugh was an unsuitable contender for the diving work you employed him to undertake, but you allowed him to take those risks to make a quick buck.
"The risk of death or serious injury was obvious to you, but your cavalier attitude towards safety was the cause of Mr Pugh's death.
"With hindsight you bitterly regret what happened."
Speaking after the hearing, Iwan Jenkins, from the Crown Prosecution Service, said Pike "stood by and watched" as Mr Pugh entered the water "knowing that safety regulations were being breached".
"His deceit and callousness resulted in Gareth losing his life," he said.
"There was clear evidence Pike had made enquiries with legitimate dive operators to cost this activity but he chose not to use them, instead falsely claiming to the golf club that he was a qualified commercial diver with his own equipment."
Mr Pugh's partner Mayree Worton said: "What upsets me the most is the bond that our daughter and Gareth had together is no longer there.
"The sentencing of Dale Pike is a relief, however it doesn't make what has happened any less painful, upsetting or distressing and it does not bring Gareth back."

The attacks, occurring from 2011 to 2013, are believed to have been co-ordinated from Iranian companies.
The US Department of Justice revealed an indictment against the seven, believed to be working for their government in Iran.
The indictment calls them "experienced computer hackers" and officials said the attacks were a "wake-up call".
It is the first time the US is charging people associated with a national government with hacking into US infrastructure for major industries like finance and water.
The attacks "threatened our economic well-being and our ability to compete fairly in the global marketplace - both of which are directly linked to our national security," said US Attorney General Loretta Lynch.
"And we believe that they were conducted with the sole purpose of undermining the targeted companies and damaging the online operation of America's free market."
Mrs Lynch said the attacks cost the victims tens of millions of dollars.
Ahmad Fathi, Hamid Firoozi, Amin Shokohi, Sadegh Ahmadzadegan, Omid Ghaffarinia, Sina Keissar and Nader Seidi are identified in the indictment as the alleged attackers.
The charges carry a maximum sentence of 10 years in prison for conspiracy to commit and aid and abet computer hacking.
It is almost certain that Iran will not send the accused to the US, and they have not been arrested.
The indictment is still important, said FBI director James Comey.
"The world is small, and our memories are long," he said. "We never say never. People often like to travel for vacation or education, and we want them looking over their shoulder."
A golf company director has been jailed after a ball collector drowned in a freezing course lake.
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The US has charged seven Iranians for allegedly hacking nearly 50 financial companies and a New York dam.