Harrison waded out as far as possible before putting his torch in his mouth and swimming the last few metres.
As he got to her she went under, he said. "Half my head was under the water and I grabbed her by the hair and pulled her up."
As the father of two emerged from the river two more officers and a police recruit arrived and helped get the teenager on to the bank.
"She wasn't quite unconscious. She was very close."
Firefighters arrived, followed by St John Ambulance paramedics who rushed the girl to Waikato Hospital where she was admitted in a serious but stable condition.
The young woman made a full recovery but Harrison has yet to meet her.
He said being recognised by the Royal Humane Society with a bronze medal for the rescue was "humbling".
His bravery is being recognised alongside Constables Roger Cvitanich and Christopher Polglase, who also pulled people from the Waikato River in separate incidents in 2014.
One of the victims, an elderly man, did not survive.
Waikato Police Acting District Commander Inspector Greg Nicholls said conditions in the river are hazardous and unpredictable, with deep water and strong currents posing a significant risk to anybody attempting a rescue.
"In choosing to risk their own lives by entering the dangerous local waters, two lives were saved, and two families were saved from the grief of losing a loved one.
"I am very proud of the actions of all three police officers and it's an honour to witness them being recognised for their bravery."
The Royal Humane Society of NZ was established in 1898 with the principle function of recognising and rewarding those who risk their own lives to save the lives of others.
Hamilton Mayor Julie Hardaker will present the awards at a ceremony at Hamilton City Council today at 1pm.
Earlier, at 10am, the Waikato Police District Pay Parade and Awards Ceremony will recognise the bravery of members of the public including a 7-year-old girl who ran across farmland to get help when her grandfather had an accident on a quad bike.
The other bravery award will go to an off-duty volunteer firefighter.