One person has died after four people have been swept down the Waikato River, north of Taupo.
A staffer said the group were swimmers "in bikinis and togs", in their early 20s.
Taupo's mayor says the drowning of a young woman swept away on Waikato River yesterday when floodgates opened is a tragedy.
But he has stopped short of calling for the Aratiatia Dam tourist attraction to be permanently closed. A safety review is being carried out.
A young woman, believed tobe in her 20s, died after she and several friends were swept down the river by rapids that surged when the dam opened about midday.
The swimmers were not visible from the road bridge, where many people gather to watch the water being released, but people at the two downstream viewing platforms saw the group and several made emergency calls to police, Taupo Sergeant Shane McNally said.
"If anyone has any cellphone footage, we're keen to look at that."
He said he understood a group of seven young men and women had been visiting Taupo for the weekend. They had met at the Flochella music festival on Lake Taupo the day before and then decided to stop at the dam for a swim the next day. Some of them had swum there in the past.
He said despite the four water releases a day in summer and warning signs, some people still swam in the pools that were left behind after the rapids had stopped flowing.
"But when the sirens sound, you get out," he said. "It's unknown why they didn't."
The dam's gates open four times a day in summer so tourists can watch the rapids from a viewing platform. The water is calm when the gates are closed but quickly rises when they open.
The section of the river near the dam is fenced off to prevent people swimming. Signs alerting people to the danger are also in place on the bank and sirens are let off before the gates open.
The Aratiatia rapids rise quickly when the dam floodgates open. Photo / Stephen Russell
he had spoken to the dam's operator Mercury Energy, which is reviewing its safety procedures after the drowning, and it appeared not much more could have been done to prevent the death.
"It's an absolute tragedy what's happened but it sounds like the systems were in place and the signs were up and the siren went off, so it's one of those unfortunate things."
Mercury Energy chief executive Fraser Whineray confirmed yesterday the sirens were working when the drowning happened.
The death follows a close call in the same spot in 2009 when two women were swept down the river after the floodgates opened and they had to be plucked to safety by kayakers.
Even with all the warnings in place it was difficult to prevent people from getting into the water, Trewavas said.
"Where you've got water people will swim. The locals who were born and bred here know how dangerous it is and then you've got the out-of-towners who are probably not so well aware."
The death had put a dampener on a sunny weekend in Taupo, which saw residents and tourists flock to the town's waterways to cool off, Trewavas said.
Great Lake Taupo was packed on Sunday when radio station ZM held New Zealand's first floating music festival, Flochella, there.
Trewavas said the festival, which 4000 people attended, went smoothly.
