He died after being transported a short distance by ambulance to the waiting rescue helicopter.
A 17-year-old girl suffering "extreme intoxication" was also being attended to when police arrived; she was alert at Grey Base Hospital yesterday and was able to assist police inquiries about the drinking incident.
Police released Mitchell's name today and confirmed he was local.
Tributes were flowing on a Facebook page set up yesterday by a family member.
"Way too young to go mate, there's no words to express how terribly sorry we are for your loss of life and for your family and friends left behind," read one tribute.
"So sad and way too young. My deepest sympathy to the Heward family at this crushing time. Mitchell was an awesome young man," said another.
Former mentors, including South Westland Area School principal Ross Brockbank, and rugby manager and family friend Jenny Keogan, also extended their sympathies to Mitchell's family.
"He was a real family kid," Mrs Keogan said.
"He was friendly and outgoing ... always happy and always smiling.
"He was a twin and he had an exceptionally close relationship with his brother. He also had a great circle of friends.
"The loss and the circumstances for the loss are absolutely tragic. It's every parent's worst nightmare."
Mrs Keogan said Mitchell, a former Wests rugby player, was loving his full-time job on a farm.Mr Brockbank said when he last spoke to Mitchell a month ago he told him the same.
"Like all young adults he was exploring his way in the world. He was a young man who had just found his way and where he wanted to go. He was enjoying working on a farm and he'd found his place, which is what you always want for your young people, to succeed. He was a good kid. We really feel for the family."
Police investigations were continuing today around who supplied the alcohol, and in what circumstances.
"We've already established where the alcohol was purchased from and by who, however, we are now looking at the issue of how it has been supplied to underage drinkers," Detective Senior Sergeant Kevin Tiernan, of the Greymouth CIB, said this morning.
A combination of alcohol, including spirits, had been purchased legitimately from a number of Hokitika outlets.
"Our investigations now are rolling in to ... who was supplying it and under what circumstances."
Mr Tiernan said it was an offence to supply alcohol to those under the age of 18.
However, at this stage no consideration had been given to any potential charges.
The results of a post-mortem examination were also still being awaited to establish the exact cause of death.
Sergeant Russell Glue, of Hokitika Police, said the victim was part of a group of about nine - some underage and some over the legal drinking age - who had been drinking at the lake.
A number of people tried to assist the teenagers before emergency personnel arrived, including local people at the lake and an off-duty doctor who was staying overnight.
- Hokitika Guardian
