A passer-by raised the alarm when they spotted the woman in waters of the River Conon, between Dingwall and Conon Bridge.
A lifeboat and Coastguard helicopter were called to the scene on Saturday evening and she was airlifted to Raigmore Hospital in Inverness.
However, the woman, who has not been named, died later.
A Police Scotland spokesman said there were not thought to be any suspicious circumstances. Her next of kin have been contacted.
It is the latest in a host of water tragedies around the country over the last 10 days.