A young man has been killed in a water-skiing accident on the far south coast of NSW, police say.

The 22-year-old man was being towed behind his father's boat on Tuross Lake, near Bodalla, about 11.30am on Sunday when he fell into the water and was hit by another boat heading in the opposite direction.

Police said the man was struck in the head by the fibreglass runabout's propeller and suffered severe head injuries.

He was taken to Moruya Hospital but died a short time later.

Police said the boat that struck the man was being skippered at the time by an unlicensed 15-year-old boy, who is yet to be interviewed by police.

The boy and the young man who died are believed to have known each other, according to reports on social media.

In NSW, a person must hold a boat driver's licence if they drive a powered vessel for recreational purposes at a speed of 10 knots (18.5 km/h) or more.

Police are investigating the crash, including how fast the boats were going at the time.

A crime scene was established at the scene and the runabout was seized for forensic examination.

The teenage boy is yet to be formally interviewed by police and no charges have been laid.

Anyone who witnessed the crash has been urged to contact the Marine Area Command, Far South Coast Police, or Crime Stoppers on 1800 333 000.