Mr Black said the lightly clad pair, a male and female in their early 20s, were on "warehouse boats" when they decided to go for a joyride about midnight, getting in to the water at the Albert Town camping ground and travelling about half a kilometre from the Albert Town bridge before getting into trouble.
A police media spokeswoman said they received the initial call just on midnight after a member of the public "thought they heard screams from people in the water ... yelling for help".
Coastguard and the harbourmaster were both alerted.
Mr Black said the harbourmaster called in jet boat operator Go Jets Wanaka to assist in the search, while police also called tasked an ambulance and a helicopter.
"There was a bit of excitement there for a while,'' he said.
A pair, both in their early 20s, were found just below the confluence of the Cardrona River - the male was on the side of the river, on a bank, while the woman was in the middle of the river, stuck in a tree.
"[She] had been there for some time, screaming her head off for help,'' Mr Black said.
The pair were eventually collected by the boat about 12.45am - the male was returned to Wanaka, while the female was flown to Lakes District Hospital.
Neither police nor St John had any information this morning about the woman's injuries.
However, Mr Black said rescuers were fortunate to not be dealing with a double fatality.
"What on earth were they doing on the river at 12.30am?
"They're very lucky given the river's flowing at over 300 cumecs.
"It's dumb, to say the least.
"I'm not impressed - I'm dismayed about the stupidity."
It was not clear if alcohol was involved.
