A coroner says the tourist who died while on a dolphin swim in the Marlborough Sounds on Tuesday most likely died of natural causes.
An American woman, 27, was on a swim with Dolphin Watch Ecotours when she was found floating face down in Tory Channel.
Christchurch Coroner Sue Johnson says provisional post mortem findings show she does not appear to have drowned.
Dolphin Watch Ecotours says it has closed its business for two days to allow staff to recover from Tuesday's events.
Company owners Dan and Amy Engelhaupt say they have operated dolphin swims for five years without incident.
