A young NSW woman whose 21st birthday cruise was marred by a brawl at Sydney Harbour says her function was not at fault.

Six people have been charged over the fracas, which erupted about 11pm on Saturday night as Lana Battaglia was celebrating her 21st with friends on board a Constellation Cruises vessel.

It had returned to the dock to offload a “severely intoxicated person” after leaving the wharf at 5.30pm, police said.

According to police, officers were called to the wharf over a separate fight and as the cruise boat was leaving, a number of people noticed a woman in the water who had jumped from the wharf.

She was taken to hospital for assessment.

But police said another fight broke out on board and a number of people were assaulted.

Ms Battaglia was stretchered off the vessel.

“I wasn’t at fault, it was nothing I did,” she told AAP on Sunday.

“It was just me celebrating my 21st and unfortunately people got involved that I didn’t know, from the city, and started trouble.”

Constellation Cruises said the company provided corporate cruises, not “party boats”, and had operated for 20 years without incident.

By the end of the night, six people were arrested.

A 23-year-old woman and two men, aged 24 and 26, were charged with affray while another 23-year-old woman was charged with common assault.

A 25-year-old woman was charged with hindering police and another 25-year-old woman was charged with assaulting police and resisting police.

They are all due to face Downing Centre Local Court on March 14.

-AAP