A tourist whose legs were slashed by a boat propeller while swimming with dolphins in the Marlborough Sounds may have survived due to her extreme fitness.

Catherine Carlyle, a doctor from South Australia, suffered several deep gashes and fractures to both legs when she was caught in blades as she climbed off a Dolphin Watch Ecotours boat.

The tour company is under fire after people claimed a guide blew a whistle to indicate it was safe to jump into the water. Her husband, Clive, watched in horror as Carlyle lost huge amounts of blood after the Friday morning accident at Ruakaka Bay. Two crew members wrapped her in blankets to stem the bleeding.

Carlyle was flown to Wellington Hospital by the Westpac Rescue Helicopter where she remained in the intensive care unit in a serious but stable condition yesterday. She is due to undergo further surgery today and might lose a leg, relatives say.

A Blenheim relative told the Marlborough Express the incident was "absolutely hideous".

The unnamed relative added: "That it could ever happen is just crazy. It's just bad news for New Zealand tourism. It's just another activity New Zealand is renowned for that has now gone wrong. The safety issues need a really hard look at."

Carlyle is described as an extreme adventurer who scaled the sixth-highest mountain in the world in 2004, the 8201m high Cho Oyu peak in the Himalayas.

Mount Gambier Bushwalkers Association Bill Rensen said: "She was extremely outdoors oriented. ... friends that have spoken with her say she is conscious and her injuries are under control.

"I imagine her fitness has helped her recover and not succumb to those injuries."

Carlyle, who is also known by her maiden name Pye, runs a GP practice in Casterton, South Australia. Her husband, a forestry scientist, was too upset to speak yesterday.

Maritime New Zealand is investigating.