Passengers on a Queenstown jetboat ride on Saturday watched stunned as a man climbed onto the bow of the boat, stripped naked and threw himself into the Kawarau River.
The driver of the Thunder Jet boat was unable to get the man back on board.
Queenstown harbourmaster Marty Black says the 27-year-old man, who is from Brisbane, was suffering from hypothermia when eventually pulled from the water.
Mr Black says the man could have died and he's praising the efforts of two jetboating companies who helped pull him out.
The tourist has been referred to the Southland District Hospital mental health unit.