Police said all 11 were wearing lifejackets and it appeared Mr Hollnsteiner and Mr Murphy succumbed to hypothermia.
Their bodies were recovered from the lake last night and were said to be about 2km apart.
Some survivors made it to an uninhabited island on the lake and others made it to shore.
Smoke was seen coming from the island, alerting people to the disaster.
An Aquanorts employee went out on the water to help while company co-owner Kylee Smith called 111.
She said everyone connected with the group was devastated after the two young people died.
"Our main concern is for the families of the survivors and the families of these people."
She said an investigation would probably shed more light on what went wrong and she could not comment in detail.
"It is an absolutely tragic event, and our hearts go out to everybody involved. It's tragic for us and for them - and our hearts and our thoughts are with the families."
Lake Tekapo Scenic Resort manager Wayne Hardaker said the lake was like "glass" in the morning but changed rapidly.
"It could have been a lot worse."
Mr Haraker saw an Aquanorts staffer trying to get to the group.
"...He noticed that the lake got very choppy, and tried to go out there, and the boat couldn't go out, because it was just too rough," he said.
The glacier-fed lake was almost always frigid, Mr Hardaker said - even on midsummer days with 30-degree temperatures, the lake was so cold "you could only stay in five minutes.
The survivors were all taken to hospital with varying levels of hypothermia.
It is understood they have been discharged and are in Timaru.
A senior staff member from Monash University travelled to New Zealand after being alerted to the incident.
"Our deepest sympathies are extended to the families , friends and colleagues during this tragic time," Monash said in a statement posted to Facebook.
"Monash is liaising directly with the students and officials here in Australia and in New Zealand, to provide support," the University added.
Mid-South Canterbury Area Commander Inspector Dave Gaskin said when the group first went out on the lake, the weather was calm. But they were hit by winds gusting up to 40 km/h.
"The boats were swamped and they were tipped into the water," he said.
"The air temperature when it happened was about 3 degrees and the water wasn't much warmer than that and they were in the water for about an hour," he said.
"I think all of them are very lucky to be alive. To spend that amount of time in water that cold is pretty difficult."
He said the group were unguided and had paddled too far from shore.
Local volunteers and emergency service workers picked up the nine kayakers and retrieved the two bodies.
Mr Gaskin said the survivors: "are obviously extremely distressed."
The Lake Tekapo area, about 245km southwest of Christchurch, is famous for recreation activities such as tramping, mountain biking, fishing, hunting, boating and skiing
