Two men were pulled unconscious from the water at Wattamolla beach on Monday after jumping from rocks.
Sutherland police believe a Glenfield man, 25, and a Guildford man, 23, caused each other to sink briefly in their struggle after they panicked when they hit the water.
Witnesses pulled the men from the water and gave first aid before paramedics arrived.
The Guildford man was airlifted to St George Hospital in a serious condition.
He has since regained consciousness and is expected to make a full recovery.
The Glenfield male was assessed at the scene but did not require hospital treatment.
Sutherland police believe neither man was able to swim.
Cliff fall at Bundeena
A Waterfall man, 58, was airlifted to safety after he fell from from a cliff at Bundeena last week.
Police believe the man was walking along The Cobblers track at 8.45am on Thursday when he fell three metres.
PolAir found the man resting on a ledge. Paramedics and officers from the Police Rescue and Bomb Disposal Unit abseiled down to help him to a lower ledge.
He was airlifted to St George Hospital with internal injuries, cuts and concussion.
