She suffered a fracture and was treated at Nelson Hospital.
"She was just trapped on an island, a big rock island in the middle of the river with rapid around it. She'd been tipped out of the kayak and gone underwater and got her foot or ankle jammed in a rock, I believe," he said.
"I heard that she'd gone under the water so whether she had swallowed a bit of water too, I don't think it was a very good experience."
Mr Douglas-Clifford flew the helicopter down to the rock and landed one skid on the side of it, while the woman was treated and brought on board.
There was a number of people in kayaks nearby and it was not known whether the woman was in a kayaking tour group.
"We just had to get her off the island. It was a swift current, so we basically landed one skid on the island and put her on the helicopter after she'd been treated. She was in a lot of pain, of course, but [the rescue] was pretty straight-forward."
Emergency services, including ambulance and police, rushed to the scene before 9am.
Acting Senior Sergeant Matthew Elliot said the site was relatively remote.
"It's a fast-flowing river and we have had to cross a few paddocks to get there," he said.
The incident was unrelated to weather.
A Nelson Hospital spokeswoman said the woman was discharged from hospital yesterday afternoon after being treated for the fracture.
