He says soon afterwards the boat was swamped and all three men were thrown into the water.
He says they clung to a chilly bin before he decided to swim for shore.
The survivor was found on the shore about 9.30am today - nine hours after the capsize.
Police did not know if the three were wearing lifejackets.
Members of the public had reported a boat in difficulties on the lake, police said.
The capsized boat could not be found in spite of a search by the Lion Foundation Rescue helicopter and the Turangi Coastguard, whose crew recovered the bodies.
- NZPA with NZHERALD STAFF