Victoria Police Senior Sergeant Nathan Ractliffe said the boat did not capsize but could not confirm if the boys were wearing life jackets as investigations were ongoing.
He said police investigators believed the boat was “motoring along and likely to have succumbed to the water conditions … subsequently throwing the two males from the boat into Lake Mulwala”.
Sgt Ractliffe said the boat stayed upright and movement in the water threw the males out of the boat, which has now been seized for further investigation.
He said witnesses saw the two boys treading water.
“A good Samaritan has actually grabbed a floatation device from a nearby resort and assisted one of those males to come back to shore,” Sgt Ractliffe said.
“The good Samaritan has then tried to go back in to assist the second male in the water but he was unable to be located.
“A number of witnesses were trying to communicate to the second male trying to keep him above water to reassure him while the other was being assisted.”
Sgt Ractliffe said the exact search location on the Victorian side of the lake was about 150-200m west of Chinamans Bend or 100m north of the (Silverwoods) resort where the incident occurred.
He said the rescued teenager was being supported by family and his community network and is assisting police with their ongoing investigation.
Police and emergency services have found it extremely difficult to undergo a number of search activities due to the weather.
Sgt Ractliffe said conditions in the next couple of days were not expected to be favourable, but police and emergency services were doing everything they could to locate the male.
Sgt Ractliffe asked people using the lake to be wary of the search.
The search will continue with police divers, Search and Rescue, air wing, water police and SES from both sides of the border involved.