A rescue boat from the M.V. Quinitsa plucked the woman from the frigid waters 1.8 kilometres north of the Buckley Bay ferry terminal sometime after 10 p.m. PT.
The terminal provides service to nearby Denman Island.
B.C. Ferries spokeswoman Deborah Marshall says at the time of the call, the ferry was docked at Denman Island unloading passengers and getting ready to tie up for the night.
"We are very proud of their actions and events like this one show that all of their training and the drills they routinely conduct are invaluable out on the water," said Marshall.
After the rescue, Marshall says the JRCC contacted the rescue boat, "and credited the crew with saving the individual's life."
The B.C. Ferries fleet of 34 vessels provide about 500 sailings a day and are often in a position to respond to marine emergencies.