Two drivers have been charged following a fatal late-night crash in which a car plunged into a weir.

Two men were in an Audi travelling on Audley Road in the Royal National Park, south of Sydney, about 1.15am on Wednesday, police said.

The Audi was believed to be near a Mercedes when it veered off the road and crashed into Audley Weir and sank, they said.

Investigators said the 20-year-old Audi driver managed to escape the car but his passenger, also a 20-year-old, did not.

About 10.20am on Wednesday, police recovered the body of a man.

The Audi was also recovered from the weir and will be taken for forensic examination.

Both the driver who crashed the Audi and an 18-year-old man who was driving the Mercedes were taken to hospital for mandatory testing, police said.

The two drivers were subsequently arrested.

The 20-year-old faces charges including dangerous driving occasioning death while the 18-year-old was charged with driving while suspended.

Both men were given conditional bail to appear before Sutherland Local Court on June 18.