Ryan Pettengell, 41, of King's Lynn, Norfolk, and Umar Balogun, 16, from London, died at Bawsey Pits, near King's Lynn, on 16 July 2013.
Mr Pettengell's partner, Lauren Cole, had swum out to save her boyfriend after seeing him get into trouble.
An inquest jury concluded that Mr Pettengell's death was an accident.
The hearing at Norwich Coroner's Court was told Mr Pettengell was with friends at the flooded quarry during the summer heatwave when he heard Umar was missing.
Mr Pettengell decided to swim out to an island to look for him, despite having broken his wrist a few weeks earlier and Ms Cole warning him not to go into the water.
After he got into difficulty, he called to her to throw him a stick or a log.
Ms Cole said she tried, but it wouldn't float.
She swam out to him, but after struggling to hold on to him, was forced to let go as he began to drag her under.
In a statement read to the inquest, she said: "I saw him swim about halfway and then he began to slow down.
"I grabbed his arm and started to pull him. I was being pulled under and I had to swim back to the side. As I swam back, I could see him going under."
Ms Cole said she saw bubbles on the surface where Mr Pettengell had been.
The inquest heard his body was found about 50m (165ft) from the shore.
Emergency services were at Bawsey Pits searching for Umar when they were alerted to Mr Pettengell's disappearance.
Firefighter Lee Broadhurst, who was responsible for search and recovery, said Mr Pettengell was likely to have been out of his depth.
PC Ryan Williams told the inquest he was there when Mr Pettengell drowned, but could not help because he was not a competent swimmer.
He said Mr Pettengell had told friends he was going to help search for Umar whose body, unbeknown to him, had already been found in a separate lake.
West Norfolk Council has since worked with the site's owners, Sibelco UK, to improve safety, the inquest heard.
Norfolk coroner Jacqueline Lake said she would prepare a report highlighting concerns about safety at the site.
Speaking outside the inquest, Mr Pettengell's best friend Wesley Moule, who was with him the day he died, said: "He was the sort of guy that if he knew someone was in trouble, he would have gone out of his way to help them out."
He said Mr Pettengell was a good swimmer and he thought he was joking when he first appeared to be in trouble.
"As soon as he didn't come back up again we realised that he wasn't and that something was seriously wrong," he said.
The girlfriend of a man who drowned at a Norfolk beauty spot trying to rescue a teenager told how she tried to save him before he disappeared underwater.