PC Nathan Lucy swam out after the woman, who'd jumped into the water from the Red Jet terminal.
Man Stabbed On Portland
A murder inquiry is under way after a man was found stabbed to death in Dorset.
Police said a woman was under arrest following the discovery on Portland.
At this stage no-one else is being sought in connection with the investigation, Dorset Police said.
Inspector Debbie Marsden said: "Dorset Police have launched a murder investigation following a report of a male being stabbed at an address in Portland.
"A female has been arrested and is assisting police with their inquiries. At this time no other persons are believed to be outstanding.
"If any person has any additional information which would assist police with their inquiries they are asked to contact Dorset Police on 101 or 01202 222 222.''
Police said they were called to an address in Park Road at 1.27am on Wednesday 28th December by a member of the public reporting a man had been stabbed.
The man who died, who is believed to be in his forties, was pronounced dead at the scene. A 44-year-old woman, from Devon, remains in police custody.
Dad-of-two Nick Medlin from Ventnor died after being assaulted outside the Rose Inn pub in the town.
A section of Parkstone Road will be affected between 9.30am and 4.30pm for three days.
A man's died in hospital after a crash in Eastleigh.
Recently Played Tracks
Deposit £10 to get a £40 Welcome Bonus - That's £50 to play bingo, slots and more!*
Over 50 tracks to make you feel-good. New album out now...
Find your local four day weather report here.
What's happening on the roads where you are?
Make Heart the soundtrack to your day and you could be a winner with great prizes up for grabs throughout the day.
Find out more about some of the companies advertising on Heart.
Get some great ideas on how to advertise your business on radio, online and on mobile.