Crew members on board a Manly Fast Ferry have rescued a wallaby seen swimming in Sydney Harbour just after 7pm on Wednesday.

Anxious crowds gathered at the nearby Manly jetty as deckhands threw a rope around the female wallaby and gradually pulled her closer until they were ready to haul her aboard.

The wallaby was then wrapped in a blanket and whisked away by Sydney Wildlife volunteer Jodi Lewis.

Ms Lewis told Fairfax Media the wallaby, whom she named "Christine", is now doing well after being left overnight to recover from her ordeal with some water and wallaby snacks.