A diving instructor drowned in a 300ft (91m) pool at a disused quarry after she became entangled in ropes and a companion was unable to free her.
Paula Blakemore 'loved' diving at Dorothea
There was also a fault with breathing equipment and a valve diaphragm had ruptured, a Gwynedd inquest heard.
The coroner recorded a verdict of accidental death on Paula Blackmore, 43, of Congleton, Cheshire, who died at Dorothea quarry in the Nantlle Valley.
Dewi Pritchard-Jones said it was caused by "a series of unfortunate events."
Diving companion Graham Owen, of Knottingley, North Yorkshire, said they were going to descend following a line from a marker buoy.
Both were "a bit nasally" and after about 6m (20ft) he signalled to abort the dive because he could not clear his ears.
But it appeared there was a problem with her re-breather and at the same time he saw the marker buoy sinking past him.
Mrs Blakemore, a mother-of-three, had been just above Mr Owen but then she vanished.
Mr Owen described how he followed a trail of bubbles and reached 40m (131ft) below the surface.
Police divers used an underwater robot to locate Mrs Blakemore
Eventually he found Mrs Blakemore clinging to a ridge in a desperate attempt to stop her descent.
"I could see rope tangled around her left leg. I tried to pull the rope off the end of her foot but I couldn't move it," he told the inquest.
Mrs Blakemore was breathing using his equipment but getting tired, and Mr Owen said he began to become tangled in the rope himself as he tried to save her.
When he freed his legs, he was disorientated for a time, then realised she had disappeared again.
"I couldn't find any bubbles," he said. He then surfaced.
Mr Blakemore said his wife was "a very competent and proficient diver" who had visited Dorothea quarry previously.
He added: "Paula loved Dorothea, she loved diving with Graham. I know he did everything he could on that day. I would dive with him tomorrow."