On Saturday, a Sonoma County Sheriff's Office helicopter responded about 12 minutes after being requested by the Marin County Fire Department for reports of two people in the water.
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The crew found a man clinging to the overturned kayak with his dog amid high winds and 3-foot swells, the Sheriff's Office said. Suffering from cold exposure, he was lifted to shore using a 100-foot rescue line.
He told rescuers his girlfriend had slipped out of her personal flotation device and sank into the water, prompting an aerial search. The helicopter crew later spotted the woman about 200 yards from the kayak, face down and being carried by the outgoing tide.
She was brought to shore, where rescue personnel began CPR until paramedics arrived. The helicopter transported her to a hospital, where she was later pronounced dead.
Authorities said her identity will be released once relatives are notified.
National Park Service rangers recovered the dog safely from the water.