The report confirms Mr Crerar's preliminary findings at an inquest in September, when he concluded Mr Martyn most likely drowned after slipping off a pontoon, or after it struck him, affecting his ability to swim.
The lake was choppy on the day Mr Martyn went for a swim to the pontoon.
He was found between the pontoon and Scotts beach.
A postmortem report concluded Mr Martyn died from asphyxia caused by drowning.
Police reported Mr Martyn was fit and healthy and a competent swimmer.
Pathologists reported the facial injuries they observed could have happened before or after Mr Martyn died.
The injuries were not sufficient to have caused death, but it was possible they caused a brief incapacitation or loss of consciousness, leading to drowning.
Mr Crerar said he accepted the pathologists' opinion.
"I consider that the bruising identified by them in their autopsy report is more likely to have occurred prior to the death of Blair Martyn.
"The probable scenario is that Blair Martyn either slipped on the pontoon or was struck by the pontoon or the ladder to the pontoon, possibly due to its movement in the choppy water conditions prevalent at the time . . .
"I recommend that, particularly in conditions which could be considered hazardous, no-one should swim unaccompanied," Mr Crerar said.
