Warning signs were set to go up the day after an Australian man drowned at Glenorchy, following a nearly identical tragedy the week before.
A police spokeswoman said the man who died on Thursday was 35-year-old Jonathan Jordan Young, of New South Wales.
Mr Young was helping a child in the water when he got into trouble himself, the spokeswoman said.
His death follows the drowning of Leeroy Kaaho (48) in nearly identical circumstances at the same spot at the mouth of the Rees River, after attempting to rescue his 10-year-old son from Lake Wakatipu.
A Queenstown Lakes District Council spokesman said signage had been arranged following Mr Kaaho’s death and was scheduled to be installed the day after Mr Young died.
Prof Chris Button, of the University of Otago School of Physical Education, said it was likely the combination of cold water shock and strong currents that caused the twin tragedies.
Cold water shock was an involuntary response lasting one to three minutes, caused by the rapid stimulation of temperature receptors, Prof Button said.
It was typically observed in water colder than 15degC, which included most of the lakes and rivers in New Zealand.
The response generally caused an involuntary gasp, followed by hyperventilation, an increase in heart rate and a drop in brain blood flow, which could make decisions difficult.
"It really does debilitate us," Prof Button said.
People affected should relax if they could, rather than struggle, and would-be rescuers should bring flotation devices, he said.
"No-one out there is Superman. We need to realise we all get affected by this."
While there had been studies on beach rips, there were fewer on lakes and rivers, which were worthy candidates for future research.
Similarly, there was a lot of emphasis on learning to swim safely in swimming pools, which were different environments from oceans, rivers and lakes, Prof Button said.
Otago Regional Council regulatory and communications general manager Richard Saunders said the ORC’s water-monitoring programme was not geared towards predicting water safety dangers.
The council would be happy to work closely with other agencies and support any work undertaken as a result of recent events, Mr Saunders said.
The deaths of both men will be referred to the coroner
