A coroner has found that an American tourist who died while swimming with dolphins in the Marlborough Sounds suffered a heart attack.
Emily Harper, 27, was found floating face down in the Tory Channel during the Dolphin Watch Ecotours trip in 2009.
A doctor on board led CPR attempts and had the use of an oxygen bottle, provided by a salmon farming business nearby.
Paramedics on board a Coastguard vessel also tried unsuccessfully to revive the woman.
Coroner Christopher Devonport says Ms Harper suffered a heart attack which caused her to lose consciousness.
In his recommendations, Mr Devonport says marine charter vessels should always carry oxygen cylinders and resuscitation equipment.
However in Ms Harper's case, he says, she would have died quickly and quietly in the water.